316 F. R. Fraprie — Chromates of Ccesium. 



The measurements follow : 



CSjCr.jO^ (Rhombohedral-hemiheclral). 



Axial ratio, a : c — 1 : 1*5549. 



Forms, r (1011), e (0112), b (1120), c (0001). 



Cleavage not observed. 



Faces. Symbols. No. Mean. Limits. Calculated. 



cr 0001 1011 11 60° 58' 60° 49-61° 29' 60° 53' 



ce 0001 0112 7 42 5 41 43-42 9 



re 101 1 0112 49 *49 10 48 9-50 13 



re 1011 1012 11 76 55 76 51-77 3 77 2 



rb 1011 1120 4 40 50 39 33-41 17 40 50 



rr 1011 0111 24 81 41 80 51-82 33 81 40 



rr 1011 0111 98 20 



Summary. 



This paper describes the preparation and crystallographic 

 properties of two modifications of caesium chromate, Cs 2 Cr0 4 , 

 of caesium bichromate, Cs„Cr„0 T , and of caesium trichromate, 

 Cs 2 Cr 3 O 10 , and leaves in doubt the existence of a second form 

 of the bichromate. 



It proves that a pressure of thirty atmospheres during the 

 process of crystallization is not sufficient to produce any meas- 

 urable difference of crystallographic axes or angles in hexagonal 

 caesium chromate, but makes it probable that it effects a change 

 of habit in the crystals. 



In conclusion I must express my thanks to Professor Theo- 

 dore W. Richards and Dr. Charles Palache of Cambridge, and 

 Professor Paul von Groth of Miinchen, for their encourage- 

 ment and advice during the progress of this investigation. 



Cambridge, Mass., and Miinchen, 1901-1903. 



