52 PHYSIOLOGICAL PHYSICS. [Chap. v. 



the negative pole. Similarly other compounds can 

 be decomposed, animal substances like blood, milk, or 

 muscle, being also acted on. Faraday investigated 

 the subject of such decomposition, and applied the 

 phraseology now used. Thus the body decomposed 

 is called the ELECTROLYTE, and the action ELECTRO- 

 LYSIS ; the positive pole is called the ANODE, the negative 

 the KATODE ; the substances that collect at the positive 

 pole are called ANIONS, those that collect at the negative 

 pole are called RATIONS. Those that collect at the 

 positive pole are supposed to be charged with negative 

 electricity, and are called ELECTRO-NEGATIVES, while 

 those collecting at the negative pole are supposed to 

 be charged with positive electricity, and are called 

 ELECTRO-POSITIVES. It is to be noted, however, that 

 the same body may at one time be electro-positive 

 and at another electro-negative. It depends on 

 the body with which it is associated. Thus sulphur 

 is electro-negative to hydrogen, but electro-positive to 

 oxygen. It is a curious fact that the separation of 

 the different elements occurs only at the electrodes, 

 and not throughout the mass of the electrolyte. 



To account for this, a theory was propounded by 

 Grotthiiss. The diagram (Fig. 27) shows its application 

 to water. Grotthiiss supposes that there is a decom- 

 position effected throughout the entire fluid, but that 

 this is followed by a recombination, except at the 

 electrodes. Thus the molecule of water in the neigh- 

 bourhood of the positive pole being split into oxygen 

 and hydrogen, the oxygen, being electro-negative, 

 attaches itself to the positive pole. Its liberated 

 hydrogen, however, seizes on the liberated oxygen of 

 a neighbouring decomposed molecule, and recombines 

 to form a molecule of water. The free hydrogen of 

 the second molecule seizes on another atom of oxygen 

 of a neighbouring molecule, and so on throughout the 

 liquid, the recombination being complete throughout 



