on the Action of Nitric Acid upon Iron. 261 



water is being decomposed are brought for a few seconds into 

 contact (the nitric acid being diluted with about 10 parts of wa- 

 ter), and then again separated, oxygen gas is no longer given 

 out at the positive iron wire, but a yellow nitrate is formed, 

 which sinks to the bottom ; if, however, the end of the iron wire 

 which has been dipped into the nitric acid is exposed to the 

 air for a moment and the circuit then closed, oxygen gas is 

 again given off from the iron. If the communication is broken 

 by means of the negative wire and again made, after a few se- 

 conds oxygen continues to be given out at the positive iron 

 wire, when the acid is very much diluted, it requires some 

 time after closing the circuit before the oxygen gas appears. In 

 whatever manner the giving out of the oxygen gas is inter- 

 rupted, it always recommences if the iron wire is exposed for 

 a short time to the air, and the circuit then formed by it in the 

 usual way. Exactly the same effects take place when diluted 

 sulphuric or phosphoric acid is substituted for nitric acid. 



In order that oxygen gas should be given off by these acids 

 at the positive iron wire, it is first necessary that the negative 

 pole should be in communication, by means of a wire, with the 

 decomposing fluid ; that one end of the iron wire should be in 

 contact with the positive pole, and the other end with the acid. 

 By any other mode of closing the circuit, oxygen gas is not 

 given out, even when the iron wire has been previously dipped in 

 diluted sulphuric or phosphoric acid. The giving out of oxygen 

 gas will be interrupted upon bi'inging the wires of the poles 

 into contact when the last-mentioned acids are used, and will 

 not return upon exposure of the iron wire to the air. No oxygen 

 gas is given out at the positive iron wire when subphosphorous 

 or phosphorous acid dissolved in water is substituted, probably 

 because it combines with the acid : when diluted alkalis are 

 used, oxygen gas is given out at the positive end, in whatever 

 way the circuit may be closed. During my experiments I 

 have observed many other singular phaenomena, v/hich I shall 

 communicate hereafter, when the circumstances under which 

 they occurred are better understood. One of these, however, 

 I will mention in conclusion: in the same nitric acid in which 

 a platina wire served for the negative pole, a quantity of hy- 

 drogen gas was given off, but when an iron wire was substituted 

 for the platina, no gas appeared. It was only when a consi- 

 derable time had elapsed after the substitution that hydrogen 

 made its appearance. 



From several of the above-mentioned facts, it appears that 

 the law formerly laid down, that oxygen gas is only given out 

 at the positive pole of a battery when it is terminated by a no- 

 ble metal, iloes not hold good ; that the same cause which reu- 



