Calculated for 





NH 4 Hg 6 Cl 11 . 



Differences, 



71-00 



0-30 



1-27 



0-14 



H. L. Wells — Ccesimn-Mercuric Ilcdides. 228 



These salts confirm the composition of all the previously 

 known alkaline-mercuric halicles, as given in the preceding 

 table, except the single compound (NHJ 2 Hg 9 Cl 20 . It is ex- 

 tremely probable, however, that the correct formula for this is 

 OT^Hg^Cl^, for Holmes obtained results slightly lower than 

 his theory in his ammonium determinations, and it would be 

 scarcely possible to distinguish between the two formulas by 

 analysis, as will be seen from the following numbers : 



Calculated for 

 (NH 4 ) 2 H g9 Cl 20 . 



Mercury .- 70-70 



Ammonium l"41 



The differences between the amounts of mercury and Caesium 

 for the corresponding formulas are 0-80 and - 85, so that it is 

 evident that the caesium compound furnishes a far better 

 means of determining the composition of the salts. 



The first type, Cs 3 HgHl 5 , is a new one. These compounds 

 are interesting as exceptions to Remsen's law concerning the 

 composition of double-halides.* 



The salt Cs 2 Hg 3 I g , although standing alone among the caesium 

 compounds, is a very well characterized body, and the com- 

 pound (]STHJ 2 Hg 3 Cl 8 . 4H 2 0, made by Holmes, belongs to the 

 same type. 



The results of the work on the caesium-mercuric salts fulfill 

 the expectations concerning the value of caesium as a means of 

 studying alkaline double-halides, for all the previously discov- 

 ered types have been made with this metal, and one besides 

 that had never been discovered. 



Preparation. 



The compounds were made by dissolving mercuric halides in 

 hot solutions of caesium halides and cooling, or in some cases 

 evaporating at ordinary temperatures, to crystallization. The 

 relative amounts of the two halides and the dilution both have 

 an important influence in determining the salt produced. In 

 most cases dilution with water is equivalent to the addition of 

 mercury, while concentration produces the same effect as the 

 addition of a caesium halide. It has been noticed, where more 

 than one salt is deposited from a solution by cooling, that the 

 salts with more mercuric halides are formed first. This shows 

 that cooling a solution may be equivalent to the addition of 

 caesium. 



There are only a few of the salts that can be recrystallized 

 unchanged from water, most of them requiring the presence of 

 an excess of caesium halide, or in two or three cases mercuric 



* Am. Chem. Jour., xi, 296; xiv, 85. 



