56 Prof. Schoenbein oti a peculiar Voltaic Condition of Iron. 



ance at the positive iron ; neither is oxygen given out at it, 

 when the circuit is closed, by plunging first one end of the 

 iron wire into the nitric acid, and by afterward sputting its 

 other end in connexion with the positive pole of the pile. In 

 both cases a nitrate of iron is formed, even in an acid con- 

 taining 400 times its volume of water; which salt may be 

 easily observed descending from the iron wire in the shape of 

 brownish-yellow-coloured streaks. 



I have still to state the remarkable fact, that if the evolution 

 of oxygen at the anode be ever so rapidly going on, and the 

 iron wire made to touch the negative electrode within the 

 acid, the disengagement of oxygen is discontinued, not only du- 

 ring the time of contact of the wires, but after the electrodes 

 have been separated from each other. A few moments hold- 

 ing the iron wire out of the acid is, however, sufficient to re- 

 communicate to it the property of letting oxygen gas evolve 

 at its surface. By the same method the wire acquires its evolv- 

 ing power again, whatever may have been the cause of its 

 loss. The evolution of oxygen also takes place in dilute sul- 

 phuric and phosphoric acids, provided, however, the circuit 

 be closed in the manner above described. It is worthy of 

 remark, that the disengagement of oxygen at the iron in the 

 last-named acids is much easier stopt, and much more difficult 

 to be caused again, than is the case in nitric acid. In an 

 aqueous solution of caustic potash, oxygen is evolved at the 

 positive iron, in whatever manner the circuit may be closed, 

 but no such disengagement takes place in aqueous solutions of 

 hydracids, chlorides, bromides, iodides, fluorides. The oxy- 

 gen, resulting in these cases from the decomposition of water, 

 and the anion (chlorine, bromine, &c.) of the other electrolyte 

 decomposed combine at the same time with the iron. 



To generalize these facts, it may be said, that independently 

 of the manner of closing the circuit, oxygen is always dis- 

 engaged at the positive iron, provided the aqueous fluid in 

 which it is immersed do not (in a sensible manner) chemically 

 act upon it ; and that no evolution of oxygen at the anode 

 in contact with iron under any circumstances takes place, if 

 besides oxygen another anion is set free possessed of a strong 

 affinity for iron. This metal having once had oxygen evolved 

 at itself, proves always to be indifferent to nitric acid of a cer- 

 tain strength, whatever may be the chemical nature of the fluid 

 in which the phsenomenon has taken place. 



I have made a series of experiments upon silver, copper, 

 tin, lead, cadmium, bismuth, zinc, mercury, but none showed 

 any resemblance to iron, for all of them were oxidized when 

 serving as positive electrodes. Having at this present mo- 

 ment neither cobalt nor nickel at my command, I could not 



