THE RUSTING OF IRON 



By W. A. DAVIS 



Much attention has been directed recently to the study of the 

 rusting of iron. Simple as the investigation of this problem 

 would at first sight appear, it is only within the past year 

 that it has been given a definite solution. The importance 

 of the question can hardly be overestimated. In rusting, all 

 those properties of iron are destroyed which make it of pre- 

 eminent value as a metal. Moreover, in view of its almost 

 universal prevalence, the change is a very costly one. It has 

 been stated that the London and North-Western Railway 

 Company lose eighteen tons of metal daily from their rails 

 owing to wear and rust — principally rust ; this representing, at 

 the present price of steel rails, a loss of nearly ^40,000 per 

 annum. In painting the Forth Bridge, where the greatest care 

 is taken to prevent rusting, an expenditure of ^2,100 per annum 

 is incurred. 1 The increased use of iron and steel in modern 

 structures makes it indispensable that an accurate knowledge 

 should be obtained of the conditions under which the metal is 

 converted, more or less rapidly, into a material which resembles 

 the earthy ores from which it was originally extracted. 



It has long been known that dry air does not cause iron to 

 rust but that if the unprotected metal is left exposed to the 

 weather, it rapidly becomes coated with the reddish-brown, 



1 I am indebted to the Secretary of the Forth Bridge Railway Company for 

 kindly furnishing me with the following particulars. The whole of the bridge 

 is painted every three years, one-third being painted per annum. Special care is 

 taken to see that all parts affected with rust are properly cleaned and that the 

 paint is laid on a clean, dry ground, each coat being allowed to dry thoroughly 

 before the next coat is applied. The paint used consists chiefly of oxide of iron, 

 red lead and boiled linseed oil. Twenty-eight painters are continuously employed 

 throughout the year, their wages amounting to £1,700. The cost of the mixed 

 paint ready for use is about ^20 per ton ; about twenty tons are used annually. 

 The part of the bridge most affected by corrosion is that from high water to 

 a height of about twenty-five feet ; such parts have to be dealt with more 

 frequently than others. 



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