THE EXISTING OP IRON AND STEEL. 
265 
same effect. On the other hand, if we suppose that hydrogen is not given off, 
and that oxygen (as Professor Tilden supposes) should be included in 
the first equation, I think it would be difficult to explain the considerable 
amount of iron that goes into solution in ordinary aerated water. The amount 
of oxygen contained in ordinary soda-water, charged under pressure, is too 
small to account for it. 
Then Professor Tilden alluded to another point, which I should perhaps have 
mentioned in the lecture, because what he said was perfectly correct and it is an 
important fact to bear m mind, namely, that when once rust lias been formed the 
further action goes on much more quickly; and there is no doubt that metallic 
iron and rust do together form a couple and something in the nature of ordinary 
electrolytic action occurs ; but I have never been able to detect the production 
of any hydrogen under these circumstances. 
He also referred to the curious figures which are produced on the surface of 
iron in rusting, indicating irregularity in the attack of the oxygen, and he men¬ 
tioned that in the case of brass he had found that if the metal was bent it was 
attacked much more at the point where the bending occurred. I am not at all 
certain that a similar examination will hold good with regard to iron; at any 
rate the following experiment has been made. Pieces of pure iron have been filed in 
various places on the supposition that where the surface was roughened the rust¬ 
ing would go on more rapidly. As a matter of fact it did not; in several cases 
it avoided altogether the part which had been filed and commenced on the smooth 
surface. So that evidently there is more to be ascertained with regard to the 
origin of the action. The specimens of iron that you see in these bottles are 
not pure iron and are only intended to illustrate the kind of action; 
but the principal experiments have been made with nearly pure iron,—that is if 
I may call iron pure which has been proved to contain not more than O’05 °/ Q of 
impurity. With such iron you still get this curious selective attack ; you still 
get the curious figures that you noticed on the surface when ordinary iron was im¬ 
mersed in water and exposed to the air. It may possibly be due, as Professor 
Tilden has suggested, to the texture of the metal. 
I was interested to hear what Mr. Webster had to say about his experiments 
on the purification of sewage by electrolytic process with iron as an electrode. 
He has asked me whether the iron dissolved in the carbonic acid gas is a carbonate. 
I think undoubtedly it must be, because if you pass oxygen, as we have done 
here, through the solution, it is found that the sediment of rust contains a con¬ 
siderable quantity of carbonate and oxide in combination, and if that solution 
evaporates in the air it behaves as you would expect ferrous carbonate to behave. 
I do not think there is any evidence that it is merely the hydroxide of iron which 
dissolved. 
Colonel Bainbridge’s statement with regard to the wear of rails is approxim¬ 
ately correct. It is a very important matter to find out under what con¬ 
ditions steel rails rust and to ascertain how they should be treated in the manu¬ 
facture so as to lead to the least amount of corrosion. When once the surfaces 
have begun to rust then, of course the corroded material is soon removed from 
the surface and the process goes on and one can readily understand how a large 
amount of metal may be lost. 
The Chairman : —Ladies and gentlemen, it now only remains for me to ask 
you to join with me in thanking Professor Dunstan for the very interesting 
lecture he has given us to-night and also in thanking the gentlemen who have so 
ably joined in the discussion (applause). 
Professor DuNSTANj:—I only wish to thank you very much for the attention 
with which you have listened to the lecture and the interest you have shown in 
the subject to which it relates (loud applause). 
