90 H. L. Wheeler — Double Ilalides of 



soluble in the strong than in the dilute halogen acids. Excess 

 of one or the other of the constituents has no effect on the 

 composition of the products obtained. The formation of 

 As 2 3 compounds was observed on treating the double halides 

 or a solution of the constituents in strong acids, with water or 

 dilute acids. The oxygen compounds are difficultly soluble 

 in dilute acids, strong acids convert the caesium and rubidium 

 compounds into the double halides. 



Method of Analysis. 



The salts were filtered on the pump and without delay were 

 carefully freed from the mother liquor by pressing on paper. 

 They were then dried in the air. In no case was water used 

 to wash them. In order to determine arsenic the salt was dis- 

 solved in the cold in HC1 sp. gr. 1*1 and hydrogen sulphide 

 passed in for about one hour ; then a little alcohol was added, 

 the whole was warmed on the water bath for a short time, in 

 order to drive off the excess of hydrogen sulphide and effect 

 the separation of the last traces of arsenious sulphide. The 

 sulphide of arsenic was collected on a Gooch filter and after 

 washing with water, alcohol and carbon disulphide it was dried 

 at 100° and weighed. Sulphuric acid was added to the filtrate 

 and the alkali-metal determined as normal sulphate by evapo- 

 rating and igniting the residue in a stream of air containing 

 ammonia. The halogens were determined in a separate por- 

 tion as silver halides in the usual manner. 



The Double Ilalides. 



Coesium and Rubidium Arsenious Chlorides: 3CsCl.2AsCl 5 

 and SRbOl. 2AsCl z . — These have a pale yellow color like the 

 corresponding antimony and bismuth double chlorides. The 

 caesium salt was obtained by dissolving 250 gms. of CsCl in dilute 

 HCl. 2 grams of As 2 3 , in dilute HCl were then added. This 

 produced a precipitate which dissolved on the addition of 

 about 2 liters of hot HCl sp. gr. 1*1. On cooling, light yel- 

 low crystals were deposited. A portion of these was recrystal- 

 lized from a strong HCl solution of AsCl 3 . The rubidium 

 salt was prepared in the same manner, except that much 

 stronger solutions were required. Saturated solutions of 

 rubidium and arsenic chlorides in 20 per cent HCl produce 

 no precipitate on mixing but if concentrated HCl is added, 

 brilliant spangles of the double salt separate. The analysis of 

 these products gave : 





