H. L. Wells— Caesium- Mercuric Halides. 229 



parts of the solution. The salt dissolves rather sparingly in 

 hot, strong alcohol and, on cooling this solution, the compound 

 CsHgBr 3 separates out. 



Calculated 

 Found. for CsHgBr 3 . 



Cesium 22-68 23'21 



The crystals thus obtained were not large enough to measure, 

 but it was probable, from microscopic examination, that they 

 were the monoclinic form of this compound. This is interest- 

 ing from the fact that it is the cubic form of CsHgCl 3 which 

 crystallizes from alcoholic solutions. 



JSTo satisfactory crops of crystals were obtained from solu- 

 tions made with CsHg 2 CI 5 and HgBr 2 together. 



The Double Iodides. 



These salts are all yellow, CsHg 2 T 5 and Cs„Hg 3 I 8 having a 

 color nearly like that of normal potassium chromate, while the 

 others become paler as the csesium chloride increases. All of 

 them are decomposed by water, forming compounds containing 

 more mercuric iodide than the original salt, or, at last, mercuric 

 iodide itself. It is therefore possible to take any one of these 

 double-salts, and, by recrystallizing from water and evaporating 

 the resulting solutions, to prepare the complete series of five 

 double-iodides, as well as the component simple iodides, with- 

 out the use of any new material. It is noticeable that the 

 iodides differ from the chlorides and bromides in not including 

 a salt that can be recrystallized continually from water. This 

 peculiarity is doubtless due to the comparative insolubility of 

 mercuric iodide. In most cases, the analyses of the salts con- 

 taining iodine show an excess of mercury and a deficiency of 

 the halogen (or halogens). It is not known whether this was 

 due to some impurity in the salts or to analytical errors. It is 

 not considered probable that inaccuracies in the analyses could 

 have caused so much variation from theory, for the methods 

 used were the. same as for the chlorides and bromides, except 

 that alcohol was used as a solvent, and, while halogens and 

 mercury were always determined in separate portions, the sum- 

 mations of the analyses were usually satisfactory. 



Cs % HgI b . — This salt, like the corresponding chloride and 

 bromide, requires for its preparation a very concentrated solu- 

 tion of the csesium halide containing a relatively small amount 

 of the mercuric compound. It crystallizes well and may be 

 obtained, either by cooling or spontaneous evaporation. The 

 crystals form peculiar, steep pyramids. 



