JACKSON AND DERBY. FERROUS IODIDE. 217 



Of these analyses I. -VIII. were made by passing sulphurous anhy- 

 dride into the aqueous solution to convert any free iodine (formed by the 

 action of air on the solution) into hydriodic acid, and to dissolve the ferric 

 hydrate, if any, formed at the same time as the free iodine ; then, after 

 driving off the excess of the sulphurous anhydride, the iodine was precip- 

 itated as argentic iodide and the iron as ferric hydrate in the usual way. 

 Analyses IX. and X. were made by simple ignition of the ferrous iodide 

 in a porcelain crucible, when it loses all its iodine and is converted into 

 ferric oxide. 



Properties of Ferrous Iodide. 



The anhydrous salt prepared as described above forms plates of a deep 

 full red color with a slight brownish tint. This color is a much more pro- 

 nounced red than any appearing among the ferric salts with the exception 

 of ferric sulphocyanate. In thicker masses it is nearly or quite black ; 

 when melted and allowed to solidify, it forms a blackish red crystalline 

 mass, which looks brown on a surface of fracture.* When the plates are 

 examined under the polarizing microscope, they give evidence that they 

 belong to one of the uniaxial systems, but the outlines of these crystals 

 are so ragged that they furnish no means of deciding to which system 

 they belong. Accordingly some of the plates immersed in ether, in which 

 they dissolve very slowly, were observed under the microscope, when the 

 formation of regular hexagonal holes was observed ; there is no doubt, 

 therefore, that the crystals belong to the hexagonal system. If the salt 

 is resublimed slowly, it can be obtained in broad thin plates with a bril- 

 liant vitreous lustre ; but on one occasion very small yellow plates were 

 formed which called to mind the "gold filings " of Serullas. The melt- 

 ing point of the substance is given by Thomson as 177° ; we have not 

 attempted to determine this point anew, as it seemed to us of little prac- 

 tical value on account of the very deliquescent nature of the salt. If 

 heated to about the fusing point of soft glass in an inert gas it sublimes 

 essentially unaltered. When sublimed in a stream of nitrogen, part of the 

 iodide is deposited in the red plates already described, the rest is carried 

 on further in the tube as a yellowish cloud, which deposits a dark reddish 

 brown amorphous powder ; this is found to be much more susceptible to 

 the action of atmospheric moisture than the red plates, but we think this 

 difference in behavior is due only to the difference in the size of the par- 



* The dark color of the ferrous iodide is not without analogy, as G. P. Baxter 

 has found in this Laboratory that ferrous bromide has a dark yellow color with a 

 greenish brown tinge. 



