16 ELECTROLYSIS. 



are identical, those of compound bodies differ. The constituent 

 parts of molecules which can neither be divided mechanically 

 nor chemically are termed atoms. The molecules of bodies are 

 animated by a continual motion, and are possessed of an initial 

 force which is constantly dependent on their temperature. In 

 solid bodies, the molecules are only possessed of a vibratory 

 motion, and cannot abandon their position of equilibrium. In 

 liquids, on the contrary, although appearing motionless, these 

 molecules turn, roll over, and knock against each other, travel- 

 ling from one point to another without being subjected to 

 return to their original position. In a gaseous state the mole- 

 cules are knocking against each other, whirling, striking the 

 walls of the vessel inclosing them, and thereby find themselves 

 outside the spheres of mutual attraction. 



The elementary atoms of compound bodies are some electro- 

 positive and the others electro-negative ; they are not invari- 

 ably united in liquids, and each passes from one molecule into 

 another, setting at liberty another atom similar to itself, and 

 which, in its turn, decomposes another molecule. As soon as a 

 current passes through a compound liquid, the molecules which 

 previously had arbitrary motions in every direction, begin to 

 shift in a regular manner. The electro-negative atoms are 

 directed towards the positive electrode, and the electro-positive 

 atoms towards the negative electrode. 



Thus, after Clausius, the atom of hydrogen which consti- 

 tutes a part of a molecule of water is not invariably connected 

 to the corresponding atom of oxygen ; but is carried away into 

 an unceasing whirling, can part from this particular atom of 

 oxygen in order to combine with a neighbouring atom of oxygen 

 and get so carried, by means of successive exchanges, to distances 

 proportionally indefinite considering the radius of activity in 

 which the phenomenon is taking place. The effect of the current 

 of electricity is to impress to these motions to these exchanges 

 a systematic tendency in virtue of which the atoms of hydro- 

 gen are directed towards the negative electrode, whereas the 

 atoms of oxygen travel towards the positive electrode.* 



Before this hypothesis was formulated, Faraday had 



* See the works of Messrs. Mascart and Joubert, Blavier, Gariel. 



