232 H. L. Wells — Ccesium- Mercuric Ilalides. 



red color of of mercuric iodide without losing their form. It 

 is probable that the spontaneous decomposition results in the 

 formation of Cs 3 Hg 2 I e and Hgl 2 . It was necessary to analyze 

 the material which had become red. 



Calculated 

 Found. for CsHg 2 I 5 . 



Caesium .... 11-4V 11-39 



Mercury 35-73 34 -25 



Iodine.. 52-93 54-36 



100-13 100-00 



The Mixed Doable-halides. 



A great deal of labor has been devoted to a study of these 

 compounds in order to find to what extent they could be pre- 

 pared. The results show that caesium chloride and mercuric 

 bromide unite readily although there is a tendency towards an 

 exchange of halogens and the formation of unmixed salts. It 

 is also noteworthy that, while there is a double chloride as well 

 as a double bromide which is not decomposed by recrystalliza- 

 tion from water, all the chloro-bromides finally yield mercuric 

 bromide when so treated. 



The number of bromo-iodides is less than that of the 

 unmixed salts, for, when attempts are made to prepare com- 

 pounds containing the larger amounts of mercuric iodide, 

 there is an exchange of halogens and almost pure double 

 iodides are produced. 



Only one compound of mercuric iodide with caesium chlo- 

 ride could be prepared. This is Cs 2 HgCl 2 I 2 , and the type 

 to which it belongs may probably be considered, on this 

 account, the most stable one of the caesium-mercuric halides. 



It is evident that the mixed salts are not as readily formed 

 as the unmixed, and that the more dissimilar the two halogens 

 are, the less tendency there is to form the mixed compounds.* 



In preparing these salts, containing two different halogens, 

 the halogen of higher atomic weight was always added in 

 combination with the mercury. The methods of preparation 

 are exactly analogous to those by which the unmixed salts are 

 made, so that most of these details will be omitted in describ- 

 ing them. 



The Chloro-bromides. 



In form these all resemble the unmixed salts between which 

 they are intermediate, and all of them are colorless except 

 CsHgClBr 2 , which is pale yellow. 



*This point is discussed in connection with the cfesium trihalides. (Wells and 

 Peufield, this Journal, III, xliii, pp. 31 and 32.) 



