■30 W. G. Mixter — Polymerization of Oxides. 



The values for the heats of formation of the oxides and 

 hydroxides of iron are 2Fe + 30 + Aq = 191-3 (Thomsen), 

 Fe + O + Aq ='68-3 (T), 2Fe(OH) 2 + O + Aq = 54-6 (T), 

 Fe + O = FeO (900°) 64'3,* 2Fe + 30 = Fe 2 3 (ignited) 

 192-2* and 2FeO (900°) + O = Fe 2 3 (ignited) + 63-7 * 



The heat of formation of ferric oxide derived from that of 

 ferrous oxide and Thomsen's value for the oxidation of ferrous 

 hydroxide is 2 X 64-3 + 54-6 = 183-2 or 9 Cal. less than that 

 of ignited ferric oxide. And the heat of oxidation of ferrous 

 hydroxide is 9*1 Cal. less than that of ferrous oxide to ignited 

 ferric oxide. Ferrous oxide does not appear to be a polymer. 

 If it is then the heat of formation of Fe 2 3 in Fe 2 3 .3H 2 is 

 less than 183-2 Cal. The heat of formation of intensely-heated 

 ferric oxide is 192-2 Cal. ; that of the oxide in precipitated 

 hydroxide is 183 Cal. The difference between these values, 

 9 Cal., is the heat of polymerization, while 5 - 5 Cal. was derived 

 from ferric hydroxide that had been heated to 160°. These 

 approximate results accord with the views of different investi- 

 gators that ferric oxide under various conditions forms complex 

 molecules. Berthelotf, from a study of ferric acetate, con- 

 cluded that " l'oxyde de fer, un fois separe des acides, prend 

 certains etats moleculaires nouveaux comparable a une con- 

 densation polymerique . . ." Wyroubouf and Verneuil;}; con- 

 sider that very complex molecules of ferric oxide exist. The 

 decreasing solubility in acid of the hydroxide as the water con- 

 tent of it falls is undoubtedly due to formation of complex 

 molecules. 



Attention is called to the statement made by other investi- 

 gators and the writerg that the heat effect of each of the three 

 atoms of oxygen in ferric oxide is the same and that the heat of 

 formation of ferric oxide at high temperatures is about three 

 times that of ferrous oxide. Since, however, part of the heat 

 is due to the formation of complex molecules of ferric oxide, 

 the heat effect of the third atom of oxygen is considerably less 

 than that of the first atom. Therefore, the union of oxygen 

 with iron conforms to the rule that the second, third or fourth 

 atom of an element combining gives less heat effect than the 

 first one. 



The term ferric hydroxide has been used for convenience in 

 this paper regardless of the question whether definite hydrates 

 of ferric oxide exist. Foote and Bradley | have shown that in 

 the hydrated oxides of iron occurring as minerals there is no 



* This Journal, xxxvi, 55, and Zs. anorg. Chem., lxxxiii, 97. 



t Ann. Chem. Phys. [3j, lxv, 177, 1862. 



i Brill. Soc. Chem. [3], xxi, 137, 1899. 



§ Loc. cit. 



| This Journal, xxxvi, 184, 1913. 



