THE CORROSION OF IRON 79 



the water, is deposited at the relatively electronegative part. 

 This film of hydrogen, forming almost instantaneously and 

 covering up the negative pole, introduces an enormous resist- 

 ance into the circuit and reduces the electric current to an 

 almost negligible strength, so that the rate at which the iron 

 passes into solution is infinitely small. 



" Oxygen dissolved in the water probably acts by oxidising 

 the hydrogen thus deposited at the negative pole — destroying 

 the polarisation — and so allowing a greater current to pass 

 between the electrically different parts of the metal. 



" If this argument is true, then commercial iron ought to 

 pass into solution, in the absence of oxygen, if it is placed in an 

 electrolyte, such as copper-sulphate solution, where, instead of 

 the non-conducting hydrogen film, there would be a conducting 

 film of metallic copper produced at the relatively electro- 

 negative pole. Experiment shows this to be true. Commercial 

 iron, when brought into contact with a solution of pure copper 

 sulphate in a vacuum, causes the immediate deposition of 

 copper on the iron just as readily as when the experiment is 

 conducted in the presence of air ; in short, all the copper is 

 removed from the solution and iron takes its place." 



Inasmuch as, ex hypothesi and in point of fact, oxygen and 

 water are non-conductors both singly and when conjoined, the 

 conditions are such, when only these are present, that an 

 appreciable electric current cannot pass. But waiving this 

 argument, the fact remains that we have no reason to suppose 

 that oxygen can, in any way, reduce the resistance of a circuit — 

 all substances which can do this are of the class commonly 

 known as electrolytes, though in reality they only become 

 electrolytes when used in conjunction with water. It can only 

 act as a depolariser — but Mr. Lambert must pursue his studies 

 of Farada}^ and perhaps of later writers also a little further in 

 order that he may understand the office of the depolariser— that 

 it not only exercises the cleansing effect to which he refers and 

 also puts a stop to all back action but, which is far more 

 important, throws energy into the circuit. Over and over 

 again, this has been pointed out ; but it is not yet part of " the 

 simple and natural development of the ideas of Faraday " now 

 in progress. However, we may hope that the doctrine may 

 soon become the belief of pioneers like Mr. Lambert. 



Apparently the part played by hydrogen polarisation is 

 vastly exaggerated. We know perfectly well how small a part 

 relatively it plays in an ordinary simple fluid cell and how 



