80 SCIENCE PROGRESS 



fluctuating is the influence it exercises ; neither does it reduce 

 the current to an almost negligible strength, though it renders 

 it aggravatingly inconstant, nor has it such an effect that the 

 rate at which the metal passes into solution is infinitely small. 



Copper sulphate not only prevents any deposition of 

 hydrogen on the negative surface but by exchanging copper 

 for hydrogen contributes energy to the circuit : at the same 

 time, owing to the deposition of copper, the resistance is 

 greatly lowered, so that the action takes place more rapidly, 

 both because the electromotive force is raised and at the same 

 time the resistance is lowered. 



But the changes pictured can only take place in an 

 electrolytic circuit and such a circuit is only possible when iron 

 is in contact not only with water and oxygen but also with an 

 electrolyte; attack by water and oxygen alone is impossible. 



In any case, the illusion under which Mr. Lambert rests, 

 "that his experiments are generally accepted as proving beyond 

 any doubt that the only essentials for the corrosion of ordinary 

 iron are water and oxygen," should be dispelled by the above 

 statements. 



But there are other points of interest in his communication 

 which deserve attention. He not only contends that he has 

 prepared chemically pure iron but states that such iron can be 

 exposed to the action of oxygen and water (even tap water) 

 during an apparently indefinite time without showing any signs 

 of corrosion. Chemical purity is not the only essential, 

 however, as will be obvious from the following statement : 



<( In the preparation of pure iron by the writer's method the 

 same sample of ferric nitrate, treated in exactly the same 

 manner throughout its conversion into iron, will not always 

 give like specimens of the metal. 



" One batch of iron will rust quite readily, whilst another 

 batch can be exposed for many months to the action of air and 

 water without showing any signs of corrosion. All the pieces 

 of the same batch behave, as a rule, in a precisely similar 

 manner. Now, any difference between the batches cannot be 

 due to differences in chemical composition. The only possible 

 variable factors are temperature of reduction and rate of cooling, 

 and so differences in the product must be of a physical and not 

 of a chemical character. 



" It is a very striking fact that the pieces of iron which will 

 not rust can also be put in solutions of copper sulphate or 



