4:64: Wells and Penjield — Thallium Triiodide and its 



thallium triiodide is a double-salt, it seems probable that many 

 other compounds, which are considered as showing higher 

 valence of elements, may in reality have the structure of 

 double-salts or "addition products." 



Thallium triiodide was first described by Nickles* who pre- 

 pared it by evaporating an etherial solution of thallous iodide 

 and iodine. Nickles states that he did not obtain it in a pure 

 condition, but that his product always contained an excess of 

 iodine. He described its crystalline form, and his results will 

 be mentioned beyond. 



"We have modified Nickles' method by using alcohol as a 

 solvent and have encountered no difficulty in obtaining a pure 

 product. The amount of iodine used was slightly in excess 

 of the calculated quantity, and the solution, produced after 

 long digestion, was evaporated over sulphuric acid until crys- 

 tallization took place. The resulting crystals were frequently 

 of large size, perfectly black with a magnificent luster which 

 was slowly lost upon exposure. A sample of the salt, simply 

 pressed upon paper, gave the following results upon analysis : 



Found. 



Thallium 34-22 



Iodine 64-80 



Calculated 

 for T1I 3 . 



34-87 

 65-13 



An examination of the crystals has shown that they are 

 orthorhombic and isomorphous with the orthorhombic alkali- 

 metal trihalides. Moreover, all the forms which have been 

 observed have also been found on the alkali-metal salts, and 

 are as follows : 



a, 100, i-l 



b, 010, i-l 



c, 001, o 



g, 012, u 



d, 011, \-i 



e, 102, \-l 



P, HI, 1 



The habit is shown in figures 1 and 2, the latter being re- 

 markably like that of Csl 3 when this had been crystallized 



* J. Pharm. [4], 1, 25. 



