426 Prof. Schoenbein on the peculiar Voltaic Conditioti of Iron 



into an aqueous solution of the common sulphate of copper, 

 in the same way as the two ends of the oxidized wire, &c. are 

 plun^^ed into common nitric acid. Under these circumstances 

 not the smallest particle of copper will be precipitated on any 

 part of the wire immersed in the said solution. This peculiar 

 state of the wire, however, lasts only so long as both ends of 

 it are in the solution ; for no sooner is the protected one 

 removed from the liquid, than the other left immersed turns 

 active, that is to say, throws down copper. In this respect, 

 therefore, there is a great difference between the action of the 

 wire in question upon the solution of blue vitriol, and that of 

 the oxidized one upon common nitric acid. This difference of 

 action implies another, namely, the impossibility of transferring, 

 within the copper solution, the peculiar state from wire to wire, 

 which it is so easy to do in nitric acid, I must not omit here 

 to state the remarkable fact, that by mixing the solution 

 of the sulphate with a comparatively small quantity of chloride 

 of sodium (common salt) the calling forth of the peculiar con- 

 dition is prevented, not only in the foregoing case, but in all 

 that will be mentioned hereafter. This fact is by no means 

 an insulated one, and depends upon the same cause as that 

 which prevents the disengagement of oxygen at the iron (whilst 

 constituting the positive electrode of the pile) from a solu- 

 tion of haloid salts, &c. Presuming that by rendering iron 

 inactive towards sulphate of copper in the way described, a 

 current would be excited the same as to its direction with that 

 produced by calling forth the peculiar state of this metal within 

 nitric acid, and having had recourse to the galvanometer, I 

 was very much struck on finding that the needle was not in 

 the least affected. The instrument I made use of in my ex- 

 periments, though indicating rather weak currents, certainly 

 does not possess the highest degree of sensibility possible, (it 

 contains about 100 coils,) but as in a scientific point of view it is 

 of very great importance to know whether the peculiar condi- 

 tion of iron can in any way be called forth without exciting 

 a current at the same time, I beg you to decide this question 

 by means of your most delicate galvanometer. If your ex- 

 periments should happen to place beyond doubt the absence 

 of any current under the before-mentioned circumstance, such 

 a result would justify the deduction of very curious inferences 

 from it, and prove in the first place that the inactivity of iron 

 has, as to its origin, nothing to do with whatwecnll a current. 

 A series of phaenomena depending upon the action of iron 

 wire (associated with peroxide of lead) upon a solution of sul- 

 phate of copper may be called forth, which exhibits a beautiful 

 analogy to that set of facts communicated to you in my letter, 



