416 SCIENCE PROGRESS 



carbonate is produced. The composition of rust in the course 

 of formation is, indeed, altogether out of harmony with the 

 hydrogen peroxide theory, since this theory postulates that 

 double the quantity of hydrogen peroxide necessary to oxidise 

 the whole of the ferrous oxide to ferric oxide is produced by the 

 action of water and oxygen on iron (see equations 3 and 4). The 

 following analysis I. shows the composition of rust freshly formed 

 in an iron tank the metal of which was alternately and in rapid 

 succession exposed to the action of air and water. Analysis II. 

 gives the composition of the same rust after eight days' exposure 

 in the form of powder to ordinary air ; compared with I., it 

 shows the readiness with which ferrous carbonate and ferrous 

 oxide undergo oxidation in ordinary air and accounts for the 

 low percentages of ferrous iron found in most samples of rust 

 by previous observers. 



It would therefore appear to be finally proved that in the 

 process of rusting, the production of hydrogen peroxide plays 

 no part ; the influence of carbonic acid in ordinary rusting is 

 shown by the large proportion of ferrous carbonate in newly 

 formed rust. But carbonic acid is not the only acid which may 

 promote the atmospheric corrosion or rusting of iron. In some 

 cases sulphurous acid or nitric acid may exert a similar influence. 

 Notably is this so in the case of the iron roofs and girders 

 of several of our railway termini ; the iron is here constantly 

 exposed to the action of steam, condensed on the cold surface of 

 the metal and charged with carbonic acid and sulphurous acid 

 produced by the combustion of the coal of the locomotives. The 

 conditions for rusting in such a case are nearly ideal and very 

 special precautions become necessary to ensure protection of 

 the metal from corrosion. The rapidity of rusting in such 

 conditions is shown by the fact that it has been found neces- 

 sary to specially support, by masonry, girders at Blackfriars 

 Station (District Railway) which have undergone severe 

 corrosion. 



Primarily the rusting of iron is the result of acid attack and 

 the conditions for rusting to occur must be the same as those 



