218 PROCEEDINGS OF THE AMERICAN ACADEMY, 



tides in the two specimens. The sublimation may take place in nitrogen, 

 carbonic dioxide, or even hydrogen, but oxygen must be carefully ex- 

 cluded, as this decomposes the iodide rapidly at not very high temperatures, 

 so that on gently heating a sample of it in a porcelain crucible in a few 

 minutes all the iodine has passed off in violet fumes, and there is left a 

 reddish brown residue of ferric oxide, which retains the shape of the 

 crystals of the ferrous iodide, and is magnetic. That this latter property 

 was not due to the presence of some magnetic oxide or metallic iron in 

 the residue was proved by dissolving it in hydrochloric acid, when a strong 

 test for ferric chloride, but none whatever for ferrous chloride, was ob- 

 tained. The iodine is so completely removed by this ignition in air that 

 the process was used as a method of analyzing the ferrous iodide (Anal- 

 yses IX. and X.). De Luca observed a similar decomposition of his 

 (white) ferrous iodide. The same decomposition of the ferrous iodide by 

 the oxygen of the air takes place slowly at ordinary temperatures ; a 

 specimen of it kept in a good desiccator gives off" enough iodine vapor in 

 time to color the air within the desiccator a distinct purple. A sample 

 of the salt was kept in a desiccator over potassic hydrate, to absorb the 

 iodine, for thirteen months, and the decomposition followed by occasional 

 weighings, when it was found that about seven eighths of the total loss 

 of iodine was given off in the first six months, but that even at the end 

 of thirteen months the decomposition was not complete, as the residue 

 still contained a little iodine, and gave tests for both ferrous and ferric 

 compounds. It follows from these observations that the salt should not 

 be allowed to stand even in a desiccator before analysis, but should be 

 analyzed as soon as possible after its preparation. 



If the salt is exposed to the atmosphere, it deliquesces quickly to a 

 brown solution. The thinner plates, when kept in a corked flask or a 

 desiccator, behaved in a very striking way ; the red plate showed at first 

 a white border around its edge, which gradually spread inward, until the 

 whole plate became white ; this change was soon followed by a liberation 

 of iodine, wliich imparted a gray or even black appearance to the mass. 

 The appearance of the iodine is undoubtedly due to the decomposition by 

 air just described, but the cause of the whitening of the crystals was not 

 so evident. The most obvious theories were, that the white substance was 

 a second modification of the ferrous iodide, or that it was produced by the 

 absorption of water, which might either form enough of the green ferrous 

 iodide containing four molecules of water of crystallization to neutralize 

 optically the red color of the anhydrous salt, or might give a definite 

 compound containing less water of crystallization than the green salt. 



