iöi 



Chemistry. — "Tke passiviU/ of metals in the light of the theovi/ 

 of allotropij." V)) Prof. A. Smits ((Jomiminicaled l)y Prof. A. 

 F. HollemAiN). 



(Goinmunicaled in the meeting of January 25 1913), 



It struck me already some time ago Uiat I lie above-mentioned 

 phenomenon, which has not been satisfactoi-ily accounted for as 3'et, 

 might be explained in a plausible way in the light of the theoi-y 

 'of allotropy. We need namely only assume that, as Llie said theory 

 requires, the metals are bnilt up as a rule of different kinds of 

 molecules, which in general have a different reactive power, so that 

 one kind of molecules will act more readily than another. In this 

 case the internal equilibrium in the surface of the metal will be 

 disturbed by chemical action, and it will now depend on the rapidity 

 with which the internal equilibrium will be restored whether or no 

 anything particular occurs. 



Let us take iron as an example, whose curve of heating of the 

 solid substance betrays the presence of different kinds of molecules ^). 

 and let us immerse this in strong nitric acid. We then notice the 

 following fact: 



One kind of molecules is quickly dissolved, the other is not. 



If it is now assumed that the oxygen split off by the nitric acid, 

 which is possibly partially dissolved in the iron, acts as a negative 

 catalyst for the setting in of the internal equilibrium, only the non- 

 dissoluble kind of molecule will be left in the surface layer of the 

 iron. If the iron plate is now taken out of the nitric acid, and 

 rinsed with water, it appears that the iron no longer yields all kinds 

 of knowMi iron reactions. The strong metastable state in the surface 

 can now however be suddenly disturbed by a blow, by the appli- 

 cation of a magnetic field, by contact with positive catalysts, and 

 in other ways; the inactive molecules are then again changed into 

 the active ones, and the ordinary iron reactions ha\ e been restored. 

 This may be demonstrated in all kinds of interesting ways. The 

 periodic abrupt variations of the potential in the case of electrolysis 

 of acids with iron as anode''), may be explained in a similar way. 

 This will, I hope, be soon discussed in a following communication. 



There are views among the earlier hypotheses, which show some 

 relationship with the explanation given here, but on account of the 



1) Cf. Benedicks "On allotropy in general and that of iron in particular. Journal 

 of the Iron and Steel hislilule" N'. 11, 1912 p. 242. 



2) Adier. Z. f. phys. Cliem. 80, 385 (191i5). 



