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TENTH ANNUAL REPORT OF 



after tins, an iron wire be connected with tlie negative pole, the iron 

 wire will become passive. 



The cord of asbestos, in the experiment. Fig. 42, being replaced by 

 a si]i1ion filled with acid, the consequence will be the same ; that is, 

 the wire immersed last will not become passive. 



The same result is obtained by connecting the vessels by a platinum 

 wire instead of a siphon. Here the galvanic polarization of the plati- 

 num is the cause of the decrease of the current. 



If the platinum wire be replaced by one of a metal which is at- 

 tacked by the acid, the cause of the weakening of the current by the 

 j)latinum disappears, and in this case the end a of the iron wire last 

 dipped in B becomes passive. 



§ 50. Passive iron in a solution of sulphate of copper.. — An iron wire 

 connected with the positive pole of a pile, and introduced into a solution 

 of sulphate of copper which is already connected with the negative pole, 

 Fig. 43, acts indifferently towards this liquid ; that is, no copper pre- 

 ci])itates on this wire, and there is no oxygen developed at its surface. 

 This passivity of iron does not appear when the circuit is closed in 

 any other Avay than that mentioned. 



An iron wire, which has been rendered passive by a single immer- 

 sion in very concentrated nitric acid, or by repeated immersions in 

 ordinary acid, also shows this passivity towards a solution of sulphate 

 of copper ; that is, it no longer possesses the power of attracting 

 oxygen from the liquid, and thus of precipitating its copper. 



Fig. 43. By repeating the experiment represented in Fig. 43, 



after having exchanged the nitric acid for a solution 

 of sulphate of copper, it appears that the passivity 

 cannot be transferred from the passive end of the wire 

 P to the other end E, as was the case with the nitric 

 acid ; that is, if the end P, made passive by immer- 

 sion in concentrated acid, be dipped in a solution of 

 sulphate of copi)er, and the end of the wire E l)e then 

 placed also in the liquid, copper will be preciT)itated 

 at E. 



Since an iron wire, connected with the positive pole 

 of a })ile, acts in an entirely different manner, Schon- 

 bein justly imagined that the experiment represented 

 by Fig. 43, made with a solution of sulphate of cop- 

 per, yielded a negative result only, because the cur- 

 rent, which should have rendered the end of the 

 wire last immersed passive, was too weak in this 

 simple battery. 



For this reason, the transfer of the passivity from 

 one iron wire to the other, which we have previously 

 mentioned, and which is represented in Fig. 44, is 

 generally not possible Avlien a solution of sulphate 

 of copper is used instead of nitric acid. 



If the current can be strengthened by making the 

 wire P more negative than a platinum or passive 

 iron wire, the transfer must also be possible in a so- 

 lution of sulphate of copper. Starting from this 



