Messrs Higgins and Draper oii Electrical Decompositions. 315 



the water ensues, and hydrogen gas is liberated. This is the 

 case with potassium and sodium. That a real decomposition of 

 the oxide has taken place appears, when we submit mercury, in 

 contact with a solution of muriate of soda, to the battery. 

 Chlorine is evolved i'rom one pole, and hydrogen, with which it 

 was before combined, uniting with the oxygen of the sodium, 

 forms water. Now, in this case, the mercury may act as a 

 kind of endless valve ; for, from the intense affinity which it 

 possesses for sodium^ it instantly allows it to penetrate, and to 

 be diffused through every part of its mass ; but, by excluding 

 the water of the solution, no action can take place on the so- 

 dium, save only on that part which exists merely at the surface 

 of the amalgam. 



There is, however, between these extremes, a class of metals, 

 ifianganese is an example, which, in a very comminuted state, 

 decompose water at common temperatures, although they can* 

 not effect it, when they are in mass. The galvanic battery can- 

 not revive any metal in solution, which is not reducible by 

 means of hydrogen gas, below a red heat ; and, in all these 

 cases, this view may in general be taken, that the electrical de- 

 composition of an oxide is produced by nascent hydrogen. If 

 peroxide of iron be exposed to a current of hydrogen, decompo^ 

 sition ensues, water is formed, and a black cinerous substance is 

 left, which, though it is a non-conductor, is pure iron, and, in 

 this state, will often inflame at 100° F. The same happens 

 when a saturated solution of protosulphate of iron is decomposed 

 by electricity, the hydrogen which would be liberated from the 

 negative pole, is expended in reducing the protoxide of iron ; 

 and the more violent the voltaic action, the more comminuted 

 will be the metallic matter produced ; and, in this state, even at 

 low temperatures, iron has the power of decomposing water. 



When the substance to be decomposed is merely moistened 

 with water, we still bring the reducing agency of hydrogen into 

 action. Hydrate of potassa is a non-conductor ; but, when a 

 new compound of it is formed with water, that compound is not 

 only a conductor of electricity, but is more readily decomposed. 

 The first object is to dissolve the surface of the hydrate in the 

 smallest possible quantity of water, so as to give it a conduct-' 

 ing power. The action produced is then sufficient to separate 



