F. It. Fraprie — Chromates of Ccesium. 315 



ated as to be useless for measurement. A single crystal pos- 

 sessed a prism zone from which blurred signals could be read to 

 within a degree or so, and this measurement and the cleavage 

 are sufficient to establish the isomorphism with potassium 

 bichromate. 



Cs 2 Cr 8 0, (Triclinic). 



Axial ratio unknown. 

 Cleavage parallel to 001, perfect. 



Cs 2 Cr 2 0, K 2 Cr 2 7 



c q' 001 Oil 66^° 67° 23' 



q b Oil 010 25 26 57 



b q 010 011 3l£ 30 46 



q c 011 001 58£ 54 54 



.An analysis of this salt gave the same result as the analysis 

 made at Harvard of the salt precipitated by sulphuric acid. 



Barium $Co0 3 



Salt taken. chromate. found. Calculated. 



0-1592 0-1661 41-20 41-55 



The occasional occurrence of orthorhombic crystals of 

 entirely different form and color to those of the orthorhombic 

 chromate, but not in sufficient quantity for investigation, sug- 

 gests the probable existence of a second . form of the bichro- 

 mate. It is hoped that further investigation of this salt may 

 be made in the near future. 



Cs 2 Or 3 O 10 , Ccesium trichr •ornate. 



On further evaporation in the desiccator of the mother 

 liquor from the bichromate, beautiful dark red rhombohedra 

 of caesium trichromate were deposited. An analysis resulted 

 as follows : 



Salt taken. 



Barium 

 chromate. 



iCx0 3 

 found. 



Calculated, 



0-1845 



0-2401 



51-39 



51-47 



The habit of the crystals, which usually have one pair of 

 rhombohedral faces very large, is apparently monoclinic, but a 

 crystal with well-developed base showed the uniaxial cross 

 very distinctly, and the measurements, although the crystals 

 were not of the best, proved the hexagonal character. The 

 trichromate is thus not isomorphous with any other trichromate. 

 Mixtures of ammonium and rubidium trichromate crystallize 

 in three systems, according to Wyroubolf,* monoclinic, ortho- 

 rhombic, and hexagonal, but the present salt is of still a fourth 

 form, trigonal. 



* Wyrouboff, Bull. Soc. franc, min., 1881, iv, 120-135. 



