THE CORROSION OF IRON AND OTHER 

 METALS: AN ADDENDUM 



The October number of the Transactions of the Chemical Society 

 contains two communications by Messrs. W. R. Dunstan and 

 J. R. Hill, the one entitled " The aerial oxidation (rusting) of 

 metals," the other "The passivity of iron and certain other 

 metals," which are of special interest as contributions to the 

 subject of corrosion discussed in previous articles in this journal. 



In his earlier publication, Dunstan came to the very definite 

 conclusion " that the presence of carbonic acid or of any acid 

 is not essential to the rusting of iron, for which only dissolved 

 oxygen and iron are the necessary conditions." In describing 

 his work, one of the points on which he laid particular stress 

 was the manner in which not only alkalies but also a variety 

 of salts, such as the potassium chromates, potassium iodide, 

 permanganate and ferrocyanide, as well as hydrogen peroxide, 

 prevent rusting. The communications under consideration are 

 devoted to a discussion of the manner in which such inhibiting 

 agents act. The conclusion now arrived at is that all agents 

 which prevent rusting render iron passive and that the inhibi- 

 tion of rusting is the direct result of the passive condition of 

 the iron. 



The tests of passivity used were (a) a solution of nitric acid 



of the relative density V2, (b) a solution containing o - 5 per cent. 



of sulphate of copper; or the iron was immersed in distilled 



water and the time noted which elapsed until rusting began. 



Certain precautions, we learn, must be taken in applying these 



tests. After the iron has been exposed to the action of the 



agent, it must be washed with distilled water and not touched 



with the hands or shaken too violently, otherwise its passivity 



is destroyed. The best method is to remove the iron from the 



solution by means of a very thin glass rod bent into a hook 



at one end. The hook is inserted into a hole previously bored 



in the sheet of iron and the iron quickly dipped two or three 



times into distilled water ; it is then transferred to the testing 



liquid and the rod removed. 



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