Wells and Penfield — Series of Caesium Trihalides. 17 



Art. TV. — On a Series of Caesium Trihalides ; by H. L. 

 Wells. Including their Crystallography / by S. L„ 

 Penfield. 



In the course of some experiments with caesium compounds, 

 bromine was added to a concentrated solution of caesium chlo- 

 ride with an astonishing result. There was instantly formed a 

 bright yellow precipitate, so dense as to nearly solidify the 

 liquid. The substance readily dissolved on warming the 

 liquid, and, on cooling it, large crystals of a yellowish-red color 

 were formed which were found to be CsClBr 2 . 



In view of the fact that KI 3 was already known,* this dis- 

 covery made it probable that a series of caesium trihalides 

 could be obtained. An attempt was accordingly made to pre- 

 pare each of the following possible members of such a series 

 containing chlorine, bromine and iodine. 



1. 



■2. 

 3. 

 4. 

 5. 



Csl 3 



CsBrI 2 



CsBr 2 I 



[CsClIJ 



CsClBrI 



6. CsCIJ 



7. CsBr 3 



8. CsClBr, 



9. CsCl s Br 

 10. [CsCIJ 



all 



' the members of the series except the two 



As a result, 

 enclosed in brackets were isolated. 



These eight trihalides are easily made, being much less solu- 

 ble than the normal halides. They crystallize beautifully, 

 have remarkably brilliant colors and some of them possess an 

 unexpected degree of stability. 



Method of preparation. 



Each of these compounds can be made by dissolving, with 

 the aid of heat, the appropriate normal caesium halide and- the 

 halogen or halogens indicated by the formula in the proper 

 amount of water, or, in the single case of CsBrI 2 , in weak 

 alcohol, and cooling to crystallization. The caesium salt used 

 in making the mixed trihalides is preferably the one which is 

 not decomposed by the halogen or halogens added. In most 

 cases the presence of an excess of the normal halide is desir- 

 able in order that the halogens, especially iodine, may readily 

 dissolve and not separate out again on cooling, but the same 

 result may also be obtained by the use of weak alcohol. 

 Details of preparation will be given for each body separately. 



* Jorgensen, J. pr. Ch., II, ii, 357 ; Johnson, J. Chem. Soc, 1877, 249. 



Am. Jour. Sci. — Third Series, Vol. XLIII, No. 253.— January, 1892. 

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