THE CORROSION OF IRON AND OTHER METALS 313 



these days to Faraday's early writings on the subject ; if his 

 pronouncements had been duly weighed the confusion that 

 now prevails could not have arisen. 



The ionic dissociation school has never yet put forward 

 any clear statement defining precisely the conditions which 

 will give rise to change : there is much talk of " solution 

 pressure " but we are never told what determines the " pressure " 

 nor are the conditions under which alone it comes into 

 operation defined; the fact is usually overlooked that no 

 action ever takes place independently not only of the solvent 

 which bathes the metal but also of the electro-negative element 

 with which it is coupled — the third necessary component in 

 the system within which change occurs. The term is little 

 more than a fagon de parler — one of the many expressions 

 coined in modern times which serve very usefully not only to 

 cloak ignorance but to convey a false impression of learning. 

 The conception is about as real perhaps as would be that 

 of a tug-of-war pressure in a set of boys standing idle along- 

 side the rope on which they will pull against one another 

 when the game is played. 



Ohm's law leaves the all-necessary third component out of 

 account, except in so far as it enters into the value of R; in 

 any case, it is clear that the part the electro-negative com- 

 ponent plays has not yet received sufficient consideration. 

 Perhaps progress in the applications of electricity depends to 

 no slight extent on a proper understanding of the function of 

 this factor : the successful solution of the great problem of 

 electrical combustion — of combustion involving the direct 

 development of electrical energy — may hang upon it. 



It is well known that a single fluid cell of the old type is 

 subject to constant polarisation and that different combina- 

 tions in which a given positive element is associated with 

 different negative elements in turn — for example, zinc with 

 either copper or silver or platinum or carbon — give rise to 

 different average electro-motive forces : the reason being pro- 

 bably that the extent to which polarisation takes place varies 

 with the nature of the electro-negative material. 



In the Grove platinum-hydrogen, platinum-oxygen, sulphuric 

 acid cell, presumably both the oxygen and hydrogen are not 

 merely in contact with the platinum plates but in some inti- 

 mate way attached to or "alloyed" with them; otherwise it 



