92 PROCEEDINGS OF THE AMERICAN ACADEMY 



MoNOCLiNic OR Clinorhombic Antimonious Iodide. 



We have stated in Uie previous article, that, when a solution of anti- 

 monious iodide in carbonic disulphide is exposed to the atmospheric 

 air under the influence of the solar light, the compound in solution 

 undergoes a gradual oxidation, iodine is set free, and oxi-iodide of anti- 

 mony is precipitated. If, after this action has continued for twelve or 

 fourteen hours in the dii-ect sunlight, the very dark colored solution is 

 distilled over a water bath (at a temperature which, even at the end of 

 the process, should not exceed the boiling point of the solvent), the 

 greater part of the free iodine passes over with the distillate ; and, by 

 repeating the distillation several times after adding more of the solvent 

 to the residue in the retort, almost the whole of the free iodine can be 

 removed. When now the residue is again dissolved in the same 

 solvent, and the solution is allowed to evaporate spontaneously, there 

 is generally deposited, at first, a crop of the crystals of the red hex- 

 agonal iodide ; but, on decanting tlie remaining solution, we obtained, as 

 a final result, a small amount of yellow monoclinic crystals similar to 

 the one figured on Plate I. Fig. 6. These represent a tliird condition 

 of antimonious iodide, which, being more soluble in disulphide of car- 

 bon, are very easily separated from the hexagonal iodide with which 

 they are associated. 



The yield of monoclinic crystals in the process we have described is 

 uncertain and irregular; and as yet we have been unable to bring the 

 conditions of their formation wholly under command. After much 

 experimenting, liowever, we have reached a few definite conclusions. 

 To the crystals prepared as above, there frequently adhered a percep- 

 tible amount of free iodine, and we naturally questioned whetlier this 

 impurity might not have some influence on their production ; but after 

 repeatedly recrystallizing the hexagonal iodide from solutions contain- 

 ing even a large excess of free iodine, and obtaining none of the 

 monoclinic modiiication, we concluded that the iodine had no further 

 effect than to modify the habit of the hexagonal crystals as already 

 described on page 78. In like manner, finding in certain cases, when 

 crude disulphide of carbon was used, that the yield of monoclinic 

 crystals was unusually large, we at once suspected that the impurities 

 originally existing in the solvent might be the determining cause 

 of the change of conditions in the crystals deposited from it. We 

 therefore experimented with some very strong-smelling disulphide of 

 carbon which had become yellow by long exposure to light and air ; 

 but we could not obtain the monoclinic crystals, except in uncertain 



