PAPERS READ IN SECTION B 



1.— THE CORROSION OF IRON AND STEFL. 



By C. E. FAWSITT, D.Sc, Ph.D., Professor of Chemistry in the University of Sydney. 



From time to time the corrosion of iron and steel is a problem 

 brought prominently before the public as some new specific case 

 of corrosion arises, with its serious, or possibly serious, consequences. 



A considerable amount of work has been recently done on 

 .corrosion, and it appears not inopportune to review the present 

 position of the corrosion of iron and steel. 



By corrosion of a metal is meant a wearing away of the metal, 

 whether the metal is transformed by oxygen and water into oxide 

 or is dissolved by some other substance such as an acid. 



In considering any kind of corrosion, it is important at first to 

 distinguish between the behaviour of a metal in the initial stages 

 of corrosion and its behaviour when the corrosion over long periods 

 of time is considered. The initial stages of corrosion represent 

 largely the " tendency " of the metal to corrode. The tendency of 

 the metal to corrode is an important point to note in connection 

 with its actual corrosion as it is measured over long periods. It 

 should be pointed out at the outset that the tendency of a metal 

 to oxidise and its tendency to dissolve are very similar things. 

 The tendency to oxidise may be judged by the amount of heat 

 given out when the substance oxidises. The tendency to dissolve 

 is shown either in the heat given out by the solution of an equivalent 

 weight of the metal, or by the potential of the metal when 

 placed in a solution of one of its salts. In the light of such measure- 

 ments it is interesting to note that there is a very close analogy 

 between the tendency to oxidise and the tendency to dissolve. 



Tendency to dissolve or oxidise is only one of many factors 

 in corrosion. Iron has less tendency to dissolve or to oxidise than 

 zinc or aluminium, and yet it will rust on until it is completely 

 oxidised, while zinc or aluminium are preserved indefinitely in 

 the air. 



In considering the corrosion of a metal it has been noticed that 

 the relative rate at which two metals are dissolved by an acid is 

 not a measure of the relative rate at which water and oxygen act 

 on the metal. Iron and many other metals dissolve in hydro- 

 chloric acid evolving hydrogen. The hydrogen is evolR^ed in 

 bubbles from the surface of the metal. This is a different process 

 from the action of oxygen and water on a metal when hydrogen 

 is not evolved. 



