H. L. Wells— Caesium- Mercuric Halides. 231 



impossible to decide whether a small amount of moisture or a 

 molecule of very unstable water of crystallization was present. 

 Two samples were analyzed. A was air-dried after pressing 

 on paper ; B was quickly dried on paper. 



Found. 

 A. 



Caesium 18-81 



Mercury 29'29 



Iodine " 51-50 



Water 



Calculated 



Found. 



Calculated 



for CsHgI 3 . 



B. for 



CsHgI 3 .HoO. 



18-63 



18-25 



18-17 



28-01 



28-74 



27-33 



53-36 



50-98 



52-05 



o-oo 



2.51* 



2-45 



99-60 100-00 100-48 100-00 



Like all the other iodides, this salt is decomposed by water. 



Cs^llg^I^ is formed under widely different conditions. It is 

 most convenient to prepare it by dissolving Cs 2 HgI 4 in the 

 proper amount of hot water and cooling. It is also formed, 

 in a finely divided condition, by treating the same salt with 

 not too much cold water. The crystals vary considerably in 

 habit, but they can be readily distinguished from the other 

 iodides. A characteristic form is a triangular plate, but plates 

 of different shape and more or less elongated prisms often oc- 

 cur. The following analyses were made of separate crops. 

 Sample C was made by treating Cs 2 HgI 4 with cold water. 





, Found 



B. 



C. . 



Calculated 

 for CsjHgalg. 



Caesium 



.. 13-89 



14-14 



14-07 



14-13 



Mercury . . 



.. 33-76 





33-83 



31-88 



Iodine 



52-07 52-10 

 99-72 



52-63 



52-96 



5399 





100-86 



100-00 



Specific gravity, taken in benzol, 5 14. The salt dissolves 

 in alcohol. It is decomposed by water with the separation of 

 a part of the mercuric iodide. From the solution thus ob- 

 tained, the salts containing less mercuric iodide can be pre- 

 pared by evaporation. 



CsHg^l h . — When a hot aqueous solution of cEesium iodide is 

 saturated with mercuric iodide, this compound is formed on 

 cooling, but, under these conditions, the substance is usually 

 mixed with Hgl 2 and often with Cs 2 Hg 3 l 8 . When weak alco- 

 hol is used as a solvent, however, a pure product is obtained 

 without difficulty. It forms slender yellow prisms which be- 

 come red on standing in an aqueous mother-liquor. They are 

 more permanent in the solution when it is alcoholic, but, on 

 drying them by pressing on paper, they quickly assume thp 



* By loss at 100°. 



