420 Nichols and Franklin — Destruction of the 



been made in the published account of the above mentioned 

 investigation,* forms the subject of the present paper. 



The influence of the electric current upon the passivity of 

 iron has been known for half a century, Schoenbein having 

 described the phenomenon at some length in the well-known 

 letter to Faraday, in which the discovery of the passive state 

 was first announced. f Faraday followed up Schoenbein's work 

 with a variety of ingenious experiments of his own, and reached 

 the conclusion that the passive state is due to the formation of 

 a film of insoluble oxide upon the metal, and that the power 

 of the electric current to produce passivity in iron, which, acts 

 as a positive electrode, lies in the liberation of free oxygen upon 

 its surface. This view of the matter has been confirmed by the 

 researches of Boutmy and Chateau,:}: who pointed out the power 

 of chromic, sulphuric and permanganic acids to promote pas- 

 sivity, and by the more recent investigations of Renard,§ in 

 which it was shown that all reducing agents have a tendency to 

 destroy the passivity of iron, whereas oxidizing agents tend to 

 bring about the passive state. 



II. 



The behavior of iron in nitric acid solutions varies in the 

 most striking manner with the temperature and strength of the 

 acid and with the molecular condition of the metal. 



The active metal may be dissolved with evolution of nitrous 

 fumes and the production of a ferric salt, with the evolution of 

 hydrogen and the production of a ferrous salt, or without the 

 evolution of any gas.| 



In anticipation of similar variations in the transition from 

 the passive to the active state, it was thought best, before enter- 

 ing upon the study of the influence of magnetization upon pas- 

 sivity, to make the following preliminary experiments: 



(1). On the behavior of passive iron in cold nitric acid. — One gram 

 of powdered iron was placed in 8 CC of nitric acid, sp. gr. 1*368, 

 and allowed to stand. The metal was apparently entirely pas- 

 sive and remained so throughout the experiment. The tem- 

 perature of the solution was 20° C. Upon standing, the acid 

 began to show signs that the passivity was not complete; at the 

 end of an hour the amount of iron in solution being sufficient 

 to color the acid unmistakably. Repetitions of the experi- 

 ment, always with the same. result, led to the conclusion that in 



* On the Chemical Behavior of Iron in the Magnetic Field, this Journal, April, 

 1886, vol. xxxi, p. 272. 



f Faraday: Experimental Researches, vol. ii, pp. 237-244. 

 ± Boutmy and Chateau: Cosmos, xix, p. 117. 

 S5 Renard : Comptes Rendus, vol. lxxix, No. 5. 

 || Ordway : this Journal, II, vol. xl, p. 316. 



