102 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



cause for the disappearance of the oxygen and hydrogen which would otherwise be 

 evolved: and when hydrogen does not appear at the cathode in an aqueous solution^ it 

 perhaps always indicates that a secondary action has taken place there. No exception 

 to this rule has as yet occurred to my observation. 



779. Secondary actions are not confined to aqueous solutions, or cases where water 

 is present. For instance, various chlorides acted upon, when fused (402.), by pla- 

 tina electrodes, have the chlorine determined electrically to the anode. In many cases, 

 as with the chlorides of lead, potassium, barium, &c., the chlorine acts on the platina 

 and forms a compound with it, which dissolves ; but when protochloride of tin is 

 used, the chlorine at the anode does not act upon the platina, but upon the chloride 

 already there, forming a perchloride which rises in vapour (790. 804.). These are, 

 therefore, instances of secondary actions of both kinds, produced in bodies containing 

 no water. 



780. The production of boron from fused borax (402. 417.) is also a case of second- 

 ary action ; for boracic acid is not decomposable by electricity (408.), and it was the 

 sodium evolved at the cathode which, reacting on the boracic acid around it, took 

 oxygen from it and set boron free in the experiments formerly described. 



781. Secondary actions have already, in the hands of M. Becquerel, produced 

 many interesting results in the formation of compounds ; some of them new, others 

 imitations of those occurring naturally*. It is probable they may prove equally in- 

 teresting in an opposite direction, i. e. as affording cases of analytic decomposition. 

 Much information regarding the composition, and perhaps even the arrangement of 

 the particles of such bodies as the vegetable acids and alkalies, and organic compounds 

 generally, will probably be obtained by submitting them to the action of nascent 

 oxygen, hydrogen, chlorine, &c., at the electrodes ; and the action seems the more 

 promising, because of the thorough command which we possess over attendant cir- 

 cumstances, such as the strength of the current, the size of the electrodes, the nature 

 of the decomposing conductor, its strength, &c., all of which may be expected to have 

 their corresponding influence upon the final result. 



782. It is to me a great satisfaction that the extreme variety of secondary results 

 have presented nothing opposed to the doctrine of a constant and definite electro- 

 chemical action, to the particular consideration of which I shall now proceed. 



^ vii. On the definite nature and extent of Electro-chemical Decomposition. 



783. In the third series of these Researches, after proving the identity of electrici- 

 ties derived from different sources, and showing, by actual measurement, the extraor- 

 dinary quantity of electricity evolved by a very feeble voltaic arrangement (371. 376.), 

 I announced a law, derived from experiment, which seemed to me of the utmost im- 

 portance to the science of electricity in general, and that branch of it denominated 

 electro-chemistry in particular. The law was expressed thus : The chemical power of 



* Annales de Chimie, torn. xxxv. p. 113. 



I 



