224 H. L. Wells — Cmium-Mercuric Halides. 



halide, for their formation. Crystallization from water can 

 therefore often be used for preparing one salt from another. 



All the compounds were made with solutions of the normal 

 salts without the use of acids. Some of them have been made 

 with alcoholic solutions, but this solvent has not been found to 

 possess any advantages except for preparing CsHgJj,. 



Analytical Methods. 



The salts were always carefully examined to be sure that they 

 were not mixtures. Many mixed crops of crystals were ob- 

 tained, but I am confident that the products analyzed were 

 pure. The crystals for analysis were always quickly and thor- 

 oughly freed from the mother-liquor by pressing repeatedly 

 between smooth filter-papers, and, at the same time, they were 

 crushed to remove included liquid. During this drying process 

 the substances were exposed to the air as little as possible to 

 avoid any evaporation of the adhering liquid before its removal. 

 After the products had been dried as thoroughly as possible in 

 this way, they were usually exposed to the air for an hour or 

 two to remove the last traces of moisture, but this was not done 

 in a few cases where I wished to be certain that no easily-lost 

 water of crystallization was present. 



Portions of about one gram of substance were usually taken 

 for analysis In no case was the analysis hampered from lack 

 of material. The chlorides and bromides were readily dis- 

 solved in water, but it was necessary in analyzing the iodine 

 compounds to dissolve them in water containing alcohol. Mer- 

 cury was invariably determined as sulphide, the precipitate 

 being collected, dried at 100° and weighed on an asbestos filter 

 in a Grooch crucible. Caesium was usually determined in the 

 filtrate from the mercuric sulphide and was always weighed as 

 sulphate. In this operation the excess of sulphuric acid was 

 removed by ignition in a current of air containing ammonia, as 

 suggested by Kriiss for potassium sulphate. In some cases 

 where ctesium alone was to be determined, the substance was 

 weighed out directly into a platinum crucible, sulphuric acid 

 was added, the excess of this and the mercury were removed 

 by evaporation and heating and normal caesium sulphate was 

 weighed. The halogens were invariably determined in separate 

 portions and were weighed as silver salts. In the cases where 

 two were present, they were determined by heating the mixed 

 silver halides to constant w r eight in chlorine. 



The Double- chlorides. 



These are all white in color and are permanent when ex- 

 posed to the air. On recrvstallizing from water all of them 

 finally yield CsHgCl 3 . 



