OXIDATION OF IRON. Ill 



the bottom of the vessel. Water had been decomposed 

 and hydrogen liberated. 



I again made another experiment, which further illus- 

 trates that carbonic acid is the real determining agent of 

 the oxidation of iron. Thus a blade of steel placed in pure 

 water which had been previously deprived of all gaseous 

 mixtures by long boiling, and then allowed to cool, the metal 

 remained bright for several days ; and when any signs of 

 oxidation appeared, it was only on a few parts of the blade. 

 The careful examination of this fact led me to infer that the 

 limited action which had taken place might be attributed to 

 traces of impurity in the iron ; and this view was supported 

 by the previous observations described, on the influence 

 which minute globules of mercury exert on the oxidation of 

 iron, as well as the known influence which a few thousandths 

 of antimony, platinum, tungsten, sulphur, phosphorus, &c. 

 impart to iron — and, again, the facts I published a few years 

 ago, that by covering the one-hundredth part of a blade of 

 iron with zinc the whole of the blade is prevented from 

 rusting when plunged in soft or sea water, whilst platinum 

 under the same circumstances promotes in a marked de- 

 gree the oxidation of iron. Therefore, if a minute quan- 

 tity of a substance modifies the properties of iron so as to 

 facilitate or retard its oxidation, we may, I think, fairly as- 

 sume that any impurity in the purest steel (watch-springs) 

 may give rise to the few specks of oxide which were ob- 

 served in the steel placed in boiled distilled water. 



Whilst I was engaged in the above experiments, it oc- 

 curred to me that it might be useful to make a series with 

 the view of throwing light, if possible, on a fact stated by 

 Berzelius, and well known to alkali- and soap-manufac- 

 turers, viz. that caustic alkalies have the property, even 

 when dilute, of preventing the oxidation of iron. 



Do the alkalies possess the curious property of rendering 

 the iron " passive," or, as Berzelius has supposed, is the iron 



