NOVEL EXPERIMENTS AND FACTS 

 CONCERNING CORROSION 



By J. NEWTON FRIEND, D.Sc, Ph.D. 



Carnegie Gold Medallist 



During the last half-century the production of iron by the 

 civilised world has increased at a phenomenal rate ; so much so 

 that at the present time some seventy million tons of pig iron 

 are being annually placed upon the market. Such being the 

 case it is evident that all problems connected with the decay and 

 preservation of iron assume increasing importance as the years 

 roll by. The object of this article is to draw attention to some 

 facts concerning corrosion that are not generally known, and to 

 describe a few simple experiments capable of adaptation for class 

 demonstrational purposes. 



Inasmuch as the usual commercial forms of iron contain a 

 relatively high percentage of impurity, it will be assumed in 

 these experiments that Kahlbaum's pure iron foil is used ; other- 

 wise the results are liable to be irregular and uncertain. If the 

 foil is well rubbed with finest emery and not touched with the 

 fingers the reader should have no difficulty in obtaining fairly 

 regular and certain results. At the same time one word of 

 warning is necessary. The corrosion of iron is affected by so 

 many apparently trivial factors that it occasionally happens that 

 two experiments may be conducted under what appear to be 

 identical conditions, and yet fail to give the same results. In 

 many cases this is due to a variation in the metal itself. This is 

 particularly the case with the ordinary forms of commercial iron, 

 which usually lack the necessary homogeneity both in their 

 chemical composition and their physical condition. Again, the 

 same piece of iron should never be used twice for experimental 

 purposes, otherwise abnormal results are very liable to accrue 

 despite the most careful superficial cleaning. This is probably 

 due to the fact that the metal is slightly porous, so that minute 

 particles of foreign bodies, particularly solutions, penetrate to a 

 small depth below the metallic surface and cause a disturbing 



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