PROTECTION OF IRON AND OTHER METAL WORK. 189 
From numerous experiments made on this subject, I find 
that with dry iron there is no rusting: with wet iron and 
total absence of oxygen there is no rust; but with iron plus 
oxygen, plus water, plus carbonic acid there is rust, also 
with iron plus water and the peroxide of hydrogen, in the 
latter case the rusting occurs with or without carbonic acid. 
The chemical mechanics of the process of rusting iron I 
take to be as follows:—an atom of iron in the presence of 
a molecule each of water and carbon dioxide results in the 
production of a molecule of ferrous carbonate with the 
liberation of a hydrogen molecule. Further, two molecules 
of the ferrous carbonate so formed, meeting with oxygen 
becomes ferric oxide, ferrous carbonate remaining; while 
two molecules of carbon dioxide are set free, and the reac- 
tion begins again de novo as long as there happens to be 
any more free iron to work upon. 
Set out in symbols these two stages appear as follows :— 
Pe On o©o,—reCO, =, A, and 
2 FeCO, + O=Fe.0, + 2CO, 
The peroxide of iron, in the presence of water becomes 
hydrated, and so we finally have Fe,O; (OH.), which is 
iron rust. 
To account for the rapid rusting of iron when in free 
access to unlimited action of water, it must be borne in 
mind that the air dissolved in natural waters is far richer 
in oxygen, the amount contained being about twice as great 
as the percentage of atmospheric oxygen, hence the rapid 
action when once iron has started to rust. The specific 
gravity of iron rust is only half that of metallic iron, the 
former being from 3°8 to 3°9, while iron is 7°8; this accounts 
for the great difference in the volume of the rust compared 
with the metal, while the energy of chemical action is quite 
enough to account for the displacement of heavy stonework 
when tied or clamped by bands of iron. Rusting causes 
