320 SCIENCE PROGRESS 



is formed by the hydrolysis of this salt. It is unnecessary to 

 consider the precise manner in which the oxygen acts ; the 

 process may be exemplified empirically in the following 

 manner : 



fro T-r f C0 3 H 



2Fe (oh + <° 2 + 0H J = 2Fe j OH 



Ferrous hydroxycarbonate Ferric dihydroxycarbonate 



(C0 3 H fOH 



Fe-mH +0H, = Fe^OH + C0 3 H„ 

 lOH lOH 



Apparently rust is formed by the " condensation " of several 

 molecules of ferric hydroxide, Fe(OH) 3 — how many we do not 

 in the least know but to judge from its colour and other 

 properties the rust molecule must be regarded as a complex 

 structure. In the process the hydroxide undergoes more or 

 less complete dehydration. 



The production of rust in this manner, in solution as it were, 

 at a distance from the iron, may be demonstrated in a very 

 interesting way, as Moody has shown, by packing the lower 

 end of a glass cylinder with ordinary iron-wire nails, then 

 covering the nails with water to the depth of an inch or two 

 after placing above them a disc of white filter-paper. On 

 observing the cylinder at intervals, it is seen that the nails 

 undergo little if any perceptible change but that rust gradually 

 separates out from the liquid and settles on the paper disc 

 above them. 



When oxygen is present together with acid in a solution 

 bathing an iron surface it is included in the circuit of change 

 and acts as depolariser ; in this case no hydrogen is evolved. 

 Initially, when no ferrous salt is present, the interaction that 

 takes place is analogous doubtless to that which attends the 

 dissolution of zinc in presence of oxygen. 



C0 3 H 2 O _ fC0 3 H HO 



re- 1 - 4- • = r e ■{ 4- 



' C0 3 H 2 O ICOsH HO 



It is to be supposed that when ferrous salt is also present 

 this is at least to some extent included in the circuit of change 

 and converted into ferric salt ; thus : 



C0 3 H 2 HO Fe(C0 3 H) 2 = 2 Fe(OH)(C0 3 H) 2 



C0 3 H 2 HO Fe(C0 3 H) 2 v n v 



