278 II. L. Wheeler — Double Halides of Tellurium 



Potassium telluriiodide, 2KI . Tel 4 . < iH n O. — This com- 

 pound can most conveniently be prepared by boiling tellurium 

 iodide in a strong solution of potassium iodide in dilute hydri- 

 odic acid. The solution, filtered while hot from any undis- 

 solved tellurium iodide, deposits long black prisms on cooling. 

 These crystals attain considerable size, about 30 mm in length, 

 when a large excess of potassium iodide is used. The mother 

 liquor, on evaporation in a desiccator, deposits more of the 

 salt, but the crystals have a different habit. 



Calculated for 

 Analysis gave : 2KI . Tel 4 . 2H 2 0. 



K 8-41 8'70 8-39 7"81 



Te_._ - 12-25 12-95 12-30 12-48 



I 75-97 76-68 76-11 



H 2 3.57 3-60 



For the determination of water in this compound the crys- 

 tals were rapidly pressed on paper and immediately analyzed. 

 It was found that the salt could be dehydrated at a tempera- 

 ture between 110°-115°, the resulting anhydrous salt being 

 stable at that temperature. This was shown by an iodine 

 determination in the residue. Analysis gave 78 # 78 per cent, 

 of iodine, calculated for 2KI . Tel 4 78-94 



This salt is far more stable in the air than the corresponding 

 bromide, but the crystals lose their luster in dry air, becoming 

 dull black on account of a superficial efflorescence. 



Crystallography . 



The crystallization of the anhydrous alkali-tellurium halides 

 is isometric. The chlorides were obtained in octahedrons with 

 little or no modification, the bromides in combination of octa- 

 hedron and cube. The chlorides and bromides were measured 

 and also proved to be isotropic by examination in polarized 

 light. Of the anhydrous iodides, the rubidium salt was the 

 only one obtained in crystals, and these were too small to 

 measure, but appeared under the microscope as combination of 

 octahedron and cube. They were so opaque that they could 

 not be tested in polarized light. 



The two hydrous salts, 2KBr . TeBr 4 . 2H 2 and 2KI . Tel 4 . 

 2H 2 although analogous to each other in their composition, 

 differ in crystallization. The bromide is orthorhombic as has 

 been shown by Baker* also by Grailich and Lang in Ram m els- 

 berg's Handbuch.f That the hydrous potassium tellurium 

 bromide obtained in the present work is identical with that 

 described by the above authors is shown by measurements of 

 the crystals. The crystallization of the salt 2KI . Tel 4 . 2H 2 is 



* Loc. cit. \ Loc. cit. 



