upon Bismuth and other Metals, 307 



pole, with a battery composed of two pairs of amalgamated 

 zinc and platina plates, was introduced into nitric acid of sp. 

 gr. 1 •4? at the temperature of 75° Fahr., its solution was in- 

 stantly checked, and on breaking contact with the battery, the 

 bismuth was found to be in the peculiar state. The acid in 

 this experiment was contained in a platina capsule, which was 

 connected with the other end of the battery and formed the 

 negative pole. But on substituting for this feeble arrange- 

 ment a battery of 20 pairs of double plates, in moderate ac- 

 tion, the bismuth continued to dissolve at a sensible rate when 

 the circuit was completed (although much more slowly and 

 in a different manner than when alone), and the peculiar stale 

 was afterwards rarely developed. 



So far are these experiments from establishing a distinction 

 in the manner of development of the peculiar states of iron 

 and bismuth, that they will appear from what follows to show 

 more clearly the identity of the two cases. 



The inactive state of iron is more readily produced by 

 simply bringing it into contact with a platina surface than by 

 making it the positive pole of a couronne des tasses; for in the 

 former case, the action of the acid may be arrested after it has 

 already commenced *, while, in the latter case, it is essential 

 that the iron should be connected with the battery before it 

 is introduced into the acidf. If a more powerful battery is 

 employed, the iron acting as positive pole has been shown by 

 Dr. Faraday to be actually oxidized and dissolved while the 

 current is passing J ; but as M. Schcenbein attributes the trace 

 of iron which he has himself sometimes discovered in the li- 

 quid, to the action of the acid vapours upon the part of the 

 iron above the acid, and the conduction of the nitrate thus 

 formed down into the acid by capillary attraction §, I thought 

 it necessary to repeat the experiment in such a manner as to 

 obviate this objection. This was easily effected by attaching 

 a small piece of iron wire to a fine wire of platina, and im- 

 mersing the former completely beneath the surface of the 

 liquid, or by coating an iron wire with glass and exposing 

 simply a section of the wire to the acid. When the iron thus 

 adjusted was made the positive pole of a battery of 20 pairs 

 of plates in moderate action, it began to dissolve at a very 

 perceptible rate (oxygen gas being, however, at the same time 

 evolved from its surface), and a black crust of insoluble oxide 

 was usually formed, when the connection with the battery was 

 broken. This result was obtained with different specimens 



• Faraday, Phil. Mag., vol. ix. p. 58. f Schcenbein, Ibid., p. 55. 



X Ibid., p. 62—3. § Sec Phil. Mag., vol. x. p. 173. 



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