314 



F. R. Fraprie — Chromates of Caesium. 



The crystals vary much in habit. Often they are in the 

 form of long yellow needles with no end faces, prismatic 

 parallel to the a axis, and limited in length only by the 

 width of the dish. Several crops were composed of prismatic 

 crystals well developed on both ends, and once or twice the 

 crop was composed almost entirely of interpenetration twins, 



the twinning plane being 130, a face not observed on any crys- 

 tal. The figures show a twin and a simple crystal, a (100) 

 is rarely present and always very narrow, and the same may 

 be said of c (001), except on the twins, where it is well devel- 

 oped. The other forms are always all present and of nearly 

 equal development. The species is completely isomorphous 

 with potassium sulphate and chromate. 



Caesium bichromate, Cs 2 Ci\ O r 



On one occasion when sulphuric acid got into the solution 

 by the accidental breaking of a tube, the crop consisted wholly 

 of microscopic red crystals of caesium bichromate. These crys- 

 tals seemed to be rhombohedra with apparently parallel extinc- 

 tion, but it was not possible to determine their system on 

 account of their small size. An analysis for chromium resulted 

 as follows : 



Salt taken. 



Barium 

 chromate. 



%Ct0 3 

 found. 



Calculated. 



0-1870 s. 



0-1437 g. 



41-42 



41-55 



The salt is quite insoluble, and is precipitated by the addition 

 of sulphuric acid to a caesium chromate solution. It was later 

 prepared by adding an equivalent or more of chromic acid to 

 the solution of chromate. It is then precipitated as an orange 

 red power, much more soluble in hot water than in cold. An 

 attempt was made to crystallize it in the " Schwedischer Topf," 

 an apparatus for crystallization by very slow and uniform cool- 

 ing, but even when the fall in temperature from 100° to 20 

 extended over a period of seven days, the crystals were so stri- 



