238 Electricity and Galvanism. 



the brilliancy of its sparks, we are apt to fancy that we are dealing 

 with an energetic dose of the agent in question ; but all the electrici- 

 ty capable of being evolved from a revolution of the plate or cylinder 

 of the most powerful machine, beautiful and brilliant as may be the 

 phenomena it develops, is incalculably less than that set free by the 

 decomposition of a drop of water or a grain of salt, the real difference 

 consisting in the state of tension or elasticity of the evolved electri- 

 city. Dr. Faraday has indeed rendered it probable, that, during the 

 decomposition of nine grains of water, an amount of electricity is 

 thus set free far greater than that which is called into terrific action 

 in the production of the vivid lightning-flashes and appalling thunder- 

 sound of the dread-inspiring tempest. 



But, to descend to positive proof, it has been shown by Becquerel, 

 and subsequently by myself, in a paper read some years ago before 

 the Royal Society, that the electricity evolved during the decomposi- 

 tion of a few grains of common salt was, when properly managed, 

 capable of producing chemical changes which, in the hands of the 

 illustrious Davy, required for their demonstration the vast voltaic 

 battery of the Royal Institution. The element necessary for the 

 production of these phenomena appears to be simply a weak current 

 with continuity of action. 



Let me draw your attention to the glass vessels before you, in 

 which a few grains of common salt have been undergoing decomposi- 

 tion during the last few hours. The current evolved has been made 

 to traverse a solution of hydrochlorate of ammonia. The result of 

 this has been the decomposition of the salt, and the evolution of its 

 curious theoretical base, the compound metal, ammonium. It has in 

 the central tube appeared as an amalgam with mercury, a globule of 

 which had been previously entangled in the folds of the platinum 

 conducting wire. The compound here appears as a grey ash-coloured 

 sponge, like spongy platinum, so light as to float in water. And 

 observe another effect of these weak currents : the amalgam remains 

 in the midst of water unchanged, whilst under ordinary circumstan- 

 ces, a moment's immersion in that fluid is sufficient to destroy it; 

 the weak current which produced it is effective in retaining it un- 

 changed. By untwisting a wire I cut off this current ; chemistry 

 comes into play, the spongy amalgam vanishes amidst a torrent of 





