652 SCIENCE PROGRESS 



of metallic iron is placed in a solution of copper sulphate, iron 

 passes into solution and copper is deposited, this change being 

 of course accompanied by a transfer of electrical charge from 

 the ions of copper to those of iron. Hydrogen acts as a metal 

 and is electrolytically classed with copper in relation to iron. 

 If, therefore, we immerse a strip of iron in a solution containing 

 hydrogen ions, an exactly similar reaction will take place, iron 

 will go into solution and hydrogen will pass from the electrically 

 charged or ionic to the atomic or gaseous condition. In such 

 a system the solution of the iron and, therefore, its subsequent 

 oxidation, must be accompanied by a ' precipitation ' or setting 

 free of hydrogen. It is very well known that solutions of 

 ferrous salts, as well as freshly precipitated ferrous hydroxide, 

 are rapidly oxidised by the free oxygen of the air to the ferric 

 conditions, so that if the electrolytic theory can account for the 

 original solution of the iron the explanation of rusting becomes 

 an exceedingly simple one. 



^^ Pure Water a Solvent of Iron. — As iron has been shown 

 by Whitney, Dunstan and one of the authors, to rust in the 

 presence of pure water and oxygen alone, the electrolytic 

 theory as a fundamental cause of the wet oxidation of iron 

 must stand or fall on the determination of one crucial question, 

 viz. Does iron pass into solution, even to the slightest extent, 

 in pure water ? If iron does dissolve, the electrolytic theory 

 is so far satisfactory; if it does not dissolve, we must conclude 

 that the oxygen finds some way of directly attacking the metal. 



" Almost every one will admit that in the case of impure 

 iron, with its unhomogeneous physical and chemical constitu- 

 tion, electrolysis will supervene, but it must be remembered 

 that we are now concerned with the underlying cause of the 

 wet oxidation or hydroxylation of iron, regardless of its state 

 of chemical purity. 



" According to the dissociation theory, even the purest water 

 contains free hydrogen ions to the extent of about i gram in 

 10,000,000 litres. If iron dissolves in the purest water it should 

 be by interchange with hydrogen and as Whitney has pointed 

 out, pure water is to this extent an acid." 



Then follows an account of experiments such as have been 

 referred to, showing that no rusting took place in boiled-out 

 water until oxygen was admitted, although iron had been dis- 

 solved prior to the entry of the oxygen. It will not be easy 

 for the average reader interested in the problem under dis- 

 cussion to disentangle the meaning from the quotation just 

 given. The implication is firstly that pure water (H2O) is to 

 some extent " dissociated " or resolved into the ions H and 

 OH and that when iron is placed in contact with pure water 



