JACKSON AND DERBY. — FERROUS IODIDE. 223 



iodine to drive out the air, was heated in a covered porcelain crucible to 

 redness as quickly as possible ; four grams of iodine were then added in 

 two portions, and the heating continued until comparatively little iodine 

 vapor escaped around the edges of the cover. When cool, the product 

 was found to be a fused mass, consisting, after it had been broken out of 

 the crucible, of red scales exactly like those described earlier in this paper. 

 These scales upon exposure to the air soon turned grayish white, and 

 then deliquesced to a brown solution. We have repeated this process of 

 Carius and Wanklyn many times, and in every case the ferrous iodide 

 formed has appeared in red scales, before it had been exposed to the air 

 long enough to absorb moisture. We, therefore, are compelled to ascribe 

 the gray color mentioned by Carius and Wanklyn to the absorption of 

 water from the air, since they, like Thomson, would in the absence of 

 analyses have supposed that the red color was due to oxidation. Our 

 present knowledge, therefore, gives no reason for supposing that an- 

 hydrous ferrous iodide has any other color than red. 



Another method of preparation may be described here, as it was tried 

 to see whether a white form might not be obtained at comparatively low 

 temperatures. A small quantity of iron by hydrogen was placed in v,he 

 middle of a small glass tube, and secured by two plugs of asbestos ; an 

 excess of iodine was inserted in one end of the tube, which was then 

 filled with nitrogen and sealed at both ends. The end containing the 

 iodine and iron was then heated to 120° by means of an air bath, and 

 after most of the iodine had sublimed into the cold upper part of the tube, 

 it was reversed so that this end and the iron were heated to 120°. After 

 repeating this distillation of the iodine through the iron several times, all 

 the metal was converted into the red ferrous iodide. This is a good 

 method for preparing a specimen to be kept to show the color. Ferrous 

 iodide was also made by passing hydrogen and iodine vapor over heated 

 ferric oxide. 



Of these methods of preparation, that of Carius and Wanklyn is the 

 easiest, but it gives a product apt to be contaminated with metallic iron 

 and oxide of iron. Thomson's method is tedious, and does not give a 

 pure product, as we observed evolution of hydriodic acid toward the end 

 of the evaporation even in an atmosphere of carbonic dioxide. The 

 sealed tube method is also slow and imperfect, so that the best method, 

 if the pure salt is desired, is the heating of iron and iodine in nitrogen 

 given in the first part of this paper. 



