372 Gooch and Havens — Volatilization of Iron Chlorides 



easily reached in the second heating by the gaseous acid. The 

 amount of residue is somewhat variable, but approximates 

 under the conditions of our work to from five to ten per cent 

 of the oxide taken : thus, in one typical experiment 0*1 grm. 

 of ferric oxide left a residue which (withdrawn after cooling) 

 weighed 0*0115 grm. 



The greater portion of the ferric oxide volatilizes when sub- 

 mitted to the action of the gaseous acid at 200° quickly and 

 abundantly in the form of the greenish vapor of ferric chloride, 

 and if the operation is interrupted at this stage the residue 

 which remains is nearly black, insoluble in water, slightly 

 soluble in cold hydrochloric acid, and readily soluble in hot 

 hydrochloric acid with the formation of ferric chloride. It is 

 probably something analogous to the oxychloride which 

 Rousseau* identifies as the product of the action of water 

 upon ferric chloride at 275° to 300°. This dark residue yields to 

 the action of the hydrochloric acid at 180° to 200° only slowly, 

 but ultimately only the residue which is essentially ferrous 

 chloride remains ; thereafter little volatilization occurs within 

 the range of temperature of our experimentation — 200° to 

 500°. 



It is obvious that a reduction of iron in the ferric condition 

 to iron in the ferrous condition takes place under the conditions 

 of our work, and it is difficult to see how this can occur other- 

 wise than by the direct dissociation of ferric chloride under 

 the low partial pressure conditioned by the brisk current of 

 hydrochloric acid gas. The temperature of formation, 180° to 

 200°, is far below that at which such dissociation is supposed to 

 begin. Thus, Gruenewald and Meyerf* found, after cooling, 

 no evidence of the dissociation of ferric chloride which had 

 been heated in the Yictor Meyer vapor-density apparatus to 

 448° in contact or partial mixture with nitrogen ; but ten per 

 cent of the residue obtained by heating to 518° was in the 

 ferrous condition. Friedel and Crafts,;}: however, did see crys- 

 tals of ferrous chloride at 440° on the walls of a Dumas con- 

 tainer filled with the vapor of ferric chloride and nitrogen, the 

 former exerting a partial pressure of 0*75 ; while ferric chloride 

 volatilized into an atmosphere of chlorine without evidence of 

 dissociation. It seems rather surprising, therefore, to find so 

 large a percentage of dissociation as that shown in our experi- 

 ments at a temperature so low — 180° to 200°. Curiously, too, 

 we find, on. repeating the experiment of heating ferric oxide in 

 gaseous hydrochloric acid, that if the temperature of the oxide 

 is 450° to 500° when the brisk current of acid begins to act, the 

 whole mass of oxide is converted and volatilizes without resi- 



*Compt. Bend., cxvi, 118. f Ber. d. d. Chem. Gesell., xxi, 68*7. 



% Compt. Bend., cvii, 301. 



