82 SCIENCE PROGRESS 



method adopted by Mr. Lambert — should so differ physically 

 that one would corrode and the other would not. 



The facts point to the conclusion that the inactive samples 

 obtained by Mr. Lambert consisted of iron which in some way 

 had been rendered passive and that the effect of pressing with 

 an agate pestle was to remove a protecting layer. The deposi- 

 tion of copper at the unpressed edges of the pieces is in 

 accordance with this explanation ; as Moody has shown, rust 

 does not form initially in the iron itself, but separates from the 

 solution, so that the position taken up by the rust has no 

 special significance. 



Mr. Lambert, it should be stated, has foreseen the possibility 

 of the formation of a protective film on the surface of the metal 

 — either of an oxide or of a hydride — but he has rejected the 

 explanation. As it is not likely either that a hydride would be 

 formed or that it would be effective if formed, it is only 

 necessary to take the formation of a coating of oxide into 

 account. Mr. Lambert contemplates the possible formation of 

 such a film by the reversible decomposition of small traces of 

 water in the hydrogen used for the reduction of the iron ; he 

 therefore dried the hydrogen used in reducing the iron oxide by 

 passing it over phosphoric oxide, so as to remove all but the 

 most minute traces of water ; then the iron which was produced 

 was brought into contact with copper sulphate solution while it 

 was still in the atmosphere of hydrogen. As there was no 

 deposition of copper, he came to the conclusion that the in- 

 activity of the metal would not be accounted for by the presence 

 of a protective film of oxide. But drying the hydrogen so 

 thoroughly in such a case can only have been a work of 

 supererogation during the greater part of the operation, as 

 water is one of the products of change; it could only be effective 

 towards the close. In view of the affinity of iron and oxygen, 

 taking the behaviour of iron into account, it is more than 

 probable that in some of Mr. Lambert's experiments the metal 

 produced was superficially coated with oxide, perhaps in 

 consequence of the introduction of a little oxygen together 

 with the hydrogen. 



It would seem therefore that the argument used against 

 Moody, which was shown by him in advance to be untenable, 

 is actually applicable to Mr. Lambert's work : his results, in 

 fact, appear to be open to doubt on more grounds than one. 



