THE CORROSION OF IRON 75 



surface of the " commercial iron," such as Moody and Friend 

 have shown to be necessary, without which, as a rule, iron 

 rusts even under the conditions these workers adopted — con- 

 ditions which involved the exclusion of carbon dioxide, if not 

 absolutely, to an extent far beyond that attained to by Lambert. 



Mr. Lambert's second series of experiments, like the first, there- 

 fore, afford no proof of the validity of his contention that iron, 

 both highly purified and commercial, can rust in the absence 

 of an acid electrolyte. 



In the latter part of his account he has much to say of the 

 properties of the so-called pure iron which he prepared — not 

 a few of his statements are self-evident propositions, though 

 valuable and interesting as bringing out the influence impurities 

 exercise in conditioning change. 



Apparently the highly purified iron at his disposal was not 

 so entirely exceptional as he implies ; although it did not rust 

 perceptibly on exposure to water and air, the rust test is 

 probably a far less delicate test of purity than the acid test. 

 It was attacked slowly by a cold, very dilute solution of chlor- 

 hydric acid and dissolved readily in chlorhydric, nitric and 

 sulphuric acids on warming. It seems therefore to have been 

 less highly purified than the zinc prepared by Reynolds and 

 Ramsay, as this latter was scarcely attacked by acid. 



Pieces of the iron which had been pressed by an agate 

 pestle in an agate mortar were found to rust readily over the 

 compressed part, whilst the uncompressed pieces remained 

 bright. Mr. Lambert attributes the difference in behaviour to 

 the difference in " solution pressure " but it is sufficient probably 

 to assume that the conductivity of the metal is increased by 

 compression and that the influence of such negative impurity 

 as is present is thereby enhanced if no other explanation be 

 forthcoming. 



The object of Mr. Lambert's communication to the Faraday 

 Society is to show, he says — 



"that a simple and natural development of the ideas of 

 Faraday on electrolysis will give us the beginnings of a satis- 

 factory theory of the corrosion of iron — a theory incomplete 

 as yet, owing to the lack of experimental facts, but one which 

 is quite in accordance with well-established facts and which 

 is not affected by the question whether iron is soluble to any 

 appreciable extent in pure air-free water." 



