AND SCHONBEIN 23 



oxygen is coining off is made to touch the negative 

 pole within the liquid for a few moments, the oxygen 

 no longer appears on its surface even when the two 

 wires are separated, the nitrate being produced in- 

 stead; but in this case also the iron resumes its 

 former indifference to the oxygen if it is held in the 

 air. I have measured the quantities of the gases 

 developed in the same time at the two poles and 

 found that the volume of the oxygen collected at the 

 positive iron electrode bears to that of the hydrogen 

 produced at the negative pole the ratio 1 : 2, which 

 may serve as a further proof that under these condi- 

 tions the iron is not in the least oxidized. Iron 

 placed under the same conditions in water to which 

 sulphuric or phosphoric acid has been added, likewise 

 develops oxygen gas ; but if the metal has previously 

 been placed in water containing sulphuric acid, or if 

 the circuit is closed with the negative pole, this 

 phenomenon does not occur. If the pole wires from 

 which the gases are coming off are made to touch for 

 a moment within the liquid, then, after they are 

 separated, no further development of oxygen takes 

 place, even if the iron wire is held for some time in 

 the air. In water containing potash, the oxygen 

 always appears in the free state on the iron, in what- 

 ever manner the circuit is closed. It is hardly 

 necessary to say that the iron must be the positive 

 pole. In order to bring to a conclusion a letter 

 which is already too long, I shall stop here and take 

 the liberty of drawing your attention to some papers 

 of mine, in which the phenomena I have described 



