in 



Analysis, and Separation of Oxides of Iron, etc. 373 





due. It is hardly to be supposed that the degree of dissocia- 

 tion at 450° to 500° can be less than that at 180° to 200°, and 

 a test of the sublimate, after cooling, shows that it contains a 

 ferrous salt. Plainly, ferrous chloride (formed by dissociation) 

 has volatilized, and inasmuch as the ferrous chloride constitut- 

 ing the residue formed at 180° to 200° does not volatilize in 

 the hydrochloric acid even at 500°, it is plain that the volatility 

 of the former is not determined by the presence of the latter. 

 Apparently, the cause of the completeness of volatilization 

 must be sought in its rapidity ; and this is not an unreasonable 

 hypothesis, if one considers that an action sufficiently rapid to 

 keep above the boat an atmosphere of ferric chloride and its 

 products of partial dissociation, might naturally provide the 

 very condition which would be effective in counteracting the 

 tendency of the residue to dissociate before it volatilizes. If 

 this hypothesis is correct, it is plain that the introduction of 

 chlorine gas, the active product of dissociation, into the atmo- 

 sphere of hydrochloric acid ought to bring about the volatiliza- 

 tion of the residue of ferrous chloride, formed at 180° to 200°, 

 which refuses to volatilize in the acid alone. As a matter of 

 fact, we find by experiment that if a little manganese dioxide 

 is added to the contents of the generator, so that the hydro- 

 chloric acid may carry with it a little chlorine, every trace of 

 ferric oxide is volatilized from the boat at 180° to 200° ; and 

 the residue of ferrous chloride found at 180° to 200° when the 

 hydrochloric acid is used alone is likewise volatilized at the 

 same temperature, when the admixture of chlorine is made. 



These facts, that ferric oxide is completely volatile in hydro- 

 chloric acid gas applied at once at a temperature of 450° to 500° 

 C, and at 180° to 200° if the acid carries a little chlorine, 

 open the way to many analytical separations of iron from sub- 

 stances not volatile under these conditions. In the experiments 

 of the following table we have applied these methods to the 

 separation of intermixed iron and aluminum oxides. The 

 ferric oxide employed was made, as before, by ignition of the 

 nitrate prepared from iron deposited electrolytically by a 

 strong current passing between platinum electrodes in a solu-' 

 tion of ammonio-ferrous sulphate.* The aluminum oxide was 

 made by igniting to a constant weight the carefully washed 

 hydroxide precipitated by ammonia from a pure hydrous 

 chloride thrown down from the solution of a commercially 

 pure chloride by hydrochloric acid.f The hydrochloric acid 



* The use of an anode of commercially pure iron wire naturally facilitates the 

 operation, but in our experience the deposit thus obtained is likely to carry traces 

 of impurity. In an attempt, too, to prepare pure ferric oxide from the oxalate 

 thrown down out of ferrous sulphate with all precautions, the material obtained 

 still held traces of silica, and possibly alumina, amounting to 0-0004 grm. in 0*1 

 grm. of the oxide. 



f This Journal, II, 346. 





