258 
THE RUSTING OF IRON" AND STEEL. 
Further experiment has completely confirmed this inference. Those 
metals rust in air which are oxidised by hydrogen peroxide, whilst 
those metals which are not oxidised by hydrogen peroxide do not rust 
in air. Iron, zinc, and lead are examples of the first-class, and the 
rusting of all of these metals is stopped by contact with substances 
which prevent the formation of hydrogen peroxide. Copper, silver, 
and nickel are examples of the second class. These metals do not rust 
in air and are not oxidised by hydrogen peroxide. I may show at 
this point an experiment proving that copper is not appreciably 
oxidised by hydrogen peroxide, and, as is well-known, this metal 
scarcely oxidises or rusts in air. 
Another interesting experiment I may show now was suggested by 
the question what would happen if a piece of iron is immersed in a 
solution of hydrogen peroxide, made just alkaline, so that decomposi¬ 
tion of the peroxide occurred very slowly at the ordinary temperature. 
It seemed improbable that rusting would occur and yet some action 
seemed likely when the metal is actually in contact with the hydrogen 
peroxide. What actually happens, as you will see is, that the entrance 
of the iron into the alkaline solution causes the immediate decomposi¬ 
tion of the hydrogen peroxide into oxygen and water and the oxygen 
is seen escaping at the surface of the iron, but yet is powerless 
to combine with the iron to form rust. 
I am now naturally brought to the question as to the exact nature 
of the chemical process of rusting, which is evidently more complicated 
than has hitherto been supposed. I refrain on this occasion from 
discussing the several chemical changes which suggest themselves as 
possible, but will at once say that after a thorough investigation of 
these different actions, I have come to the conclusion that the change 
that occurs is one in which the iron in the first instance takes oxygen 
from a molecule of water forming ferrous oxide, setting free the 
hydrogen, which joins itself to a molecule of oxygen, forming 
hydrogen peroxide, and this immediately combines with the ferrous 
oxide forming “ rustA The principal action is represented in outline 
by the following equations :— 
Fe + OH g + 0 2 = jF eO+S'gOs 
2 FeO + H 2 0 o = 2 FeO (0H) S 
It can hardly be doubted that the action is partly, if not wholly 
electrical, in its origin, as indeed we believe all chemical changes are 
fundamentally, and it is worth noting in this connection that, if 
metallic iron is made the positive pole of an electrolytic cell of water, 
“ rust ” is rapidly formed on the surface of the metal, as you see in the 
experiment now proceeding on the table. 
I now turn for a few moments to the rusting of steel, which as is 
well-known, rusts less readily than pure iron. Steel is made by the 
addition of carbon to iron, so that more or less (from '2 to 2 per cent.) 
enters into combination with the iron forming a carbide probably 
having the composition Fe s G. Steel, therefore, may be regarded as 
