Mr. Faraday o« the peculiar Voltaic Conditioii of Iron. 123 



which do the same, were published before them. The results 

 obtained by the former, extracted from a private journal dated 

 August 1825, were first published in 1833*. He describes 

 the action of nitric acid on iron ; the altered state which the 

 metal assumes; the superficial character of the change; the 

 effect of the contact of other metals in bringing the iron back 

 to its first state ; the power of platina in assisting to bring on 

 the altered or prepared state ; and the habits of steel in nitric 

 acid : he attributes the phsenomena to a certain j)ermanent elec- 

 tric state of the surface of the metal. I should recommend the 

 republication of this paper in the Philosophical Magazine. 



Professor Daniell, in his paper on Voltaic Combinations f 

 (Feb. 183C>), found that on associating iron with platina in a 

 battery charged with nitro-sulphuric acid the iron would not 

 act as the generating metal, and that when it was afterwards 

 associated with zinc it acted more powerfully than platina it- 

 self. He considers the effect as explicable upon the idea of a 

 force of heterogeneous attraction existing between bodies, and 

 is inclined to believe that association with the platina cleanses 

 the surface of the iron, or possibly causes a difference in the 

 mechanical structure developed in this particular position. 



In my letter, therefore, as published in the Philosophical 

 Magazine for the present month (July), what relates to the 

 preserving power of platina on iron ought to be struck out, as 

 having been anticipated by Sir John Herschel, and also much 

 of what relates to the action of silver and iron, as having been 

 formerly recorded by Keir. The facts relating to gold and 

 carbon in association with iron ; the experimental results as 

 to the electric currents produced ; the argument respecting 

 the chemical source of electricity in the voltaic pile; and my 

 opinion of the cause of the phasnomena as due to a relation 

 of the superficial particles of the iron to oxygen, are what 

 remain in the character of contributions to our knowledge of 

 this very beautiful and important case of voltaic condition 

 presented to us by the metal iron. 



I am, my dear Sir, yours very truly, 



E. W. Braylcy, Esq. M. Faraday. 



London Instilulion. 



* Annales de Chimie ct de Physique, \%?>?i, vol. liv. i). 87. 

 + Phil. IVaiis. 183G, p. 114.' 



P2 



