14 KANSAS ACADEMY OF SCIENCE. 



the iron being in the passive state. While in the magnetic field the iron was touched 

 with the bulb of a thermometer used in the determination of the temperature of the 

 solution. Thereupon it lost its passivity, and the solution burst into violent effer- 

 vescence. The reaction continued until the beaker was removed from the field, when 

 the iron again became passive. Investigation showed that this change of condition 

 was due to the action of the magnet, occurring instantly in solutions of high tem- 

 perature or of small degrees of concentration, and taking place upon stirring within 

 the field, even in the case of iron in cold concentrated acid. Mention of this fact 

 has been made in the published account of the above-mentioned experiments. ^ 



The further study of the phenomenon 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; Schonbein having described it in a letter to Faraday, in which 

 the discovery of the passive state was first announced, as follows : 



"... I was very curious to know in what manner iron would be acted upon by nitric acid 

 when used as an electrode. For this purpose I made use of that form of the pile known as the couronne 

 des tosses, consisting of fifteen pairs of zinc and copper. A platina wire was connected with (what we 

 call) the negative pole of the pile, an iron wire with the positive pole. The free end of the platina 

 wire was first plunged into nitric acid, sp.gr. 1.35, and by the free end of the iron wire the circuit 

 closed. Under these circumstances the iron was not in the least affected by the acid; and it remained 

 indiflferent to the fluid not only as long as the current was passing through it, but even after it had 

 ceased to perform the function of a positive electrode. The iron wire proved, in fact, to be possessed of 

 all the properties of what we have called a passive one. If such a wire is made to touch the negative 

 electrode, it instantly becomes active, and a nitrate of iron is formed ; whether separate from the pos- 

 itive pole or still connected with it, and whether the acid be weak or strong." - 



Faraday^, as is well known, followed up Schonbein's work with a variety of in- 

 genious experiments of his own, and reached the conclusion that the passive state 

 is due to the formation of an insoluble film of 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 at the surface of the metal. If Fara- 

 day's theory needed other confirmation than that afforded by his own varied experi- 

 ments and those of Schonbein, it has received support from the work of Boutmy and 

 Chateau* who pointed out the power of chromic, sulphuric and permanganic acids 

 to promote passivity, and from the more recent researches of Renard^, in which it 

 was shown that reducing agents have a tendency to destroy the passivity of iron, 

 while oxydizing 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 solution, 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 formation of 

 a ferrous salt, or without the evolution of any gas; the character of the reaction de- 

 pending upon strength of acid and temperature." In anticipation of similar varia- 

 tions in the transition from the passive to the active state, it was thought best before 

 undertaking the study of the influence of magnetism upon passivity, to make the 

 following preliminary experiments. 



1. — On the behavior of passive iron in cold nitric acid. 



One gram of iron was placed in 8 cc. of nitric acid ( 1.368) and allowed to stand. 



' On the Chemical Behavior of Iron in the Magnetic Field : Am. .Tour. Sci., vol. 31, April, 1886. 



■'Experimental Researches of Faraday. Vol. II, p. 237; also I'hilosojihical Magazine, May, 1836. 



^Faraday; Experimental Researches. Vol. II, p. 244. 



' lioutmy and Cliateau ; Cosmos, XIX, p. 117. 



'■■Renard; Comptes Kendus. Vol. 7'J, No. 5. 



«Ordway; American Journal of Science. II Vol. XL, p. 316. 



