Arsenic with Ccesium and Rubidium. 



97 





Measured. 



Calculated, 



c * c (twin) 0001 ^0001 



70° 45' 



70° 44' 



c * r 0001^1011 



54 40 



54 38 



r*m 1011 /s 1010 



*35 22 





r*z 1011 ^ 0111 



48 14 



48 H 



«U2 1010^0111 



65 34 



65 56 



3 Csl. 2AsI z . — This salt was made in beautiful crystals up to 

 3 mm in length. The forms observed are p and a. The habit 

 is that of a steep doubly terminated hexagonal pyramid, with 

 the basal planes small or wanting. Often the middle edges 

 are rounded by oscillatory combinations of the pyramids giv- 

 ing rise to horizontal striations. There was no indication of a 

 prism or of a rhombohedral development of the pyramidal 

 faces. 







Measured. 



Calculated. 



c *p 



0001^2021 



*70° 49' 





P*P 



2021^2021 



38 19 



38° 22' 



p^p 



2021 a 0221 



56 24£ 



56 21 34' 



This salt is without optical anomalies and no pleochroism 

 was observed. 



SJRbl. 2AsI r — This salt was prepared in very small crystals, 

 not over l mm in length. The forms observed were c, m and^>. 

 The habit is similar to fig. 6 but usually the middle edges are 

 replaced by the faces of the prism m or are rounded by hori- 

 zontal striations. 







Measured. 



Calculated, 



p~ p 



2021 ^ 0221 



*56° 21' 





c * p 



0001^2021 



70 47 



70° 



P Affl 



2021 ^ 1010 



19 12 



20 56' 



Optically, this salt shows anomalies. Basal cleavage plates 



between crossed nicols are not dark but light and remain so 



during revolution. In convergent light the locus of an optic 



axis is seen in the center of the field coinciding with the ver- 



Ai£. Jour. Sci.— Third Series, Yol. XLYI, No. 272.— August, 1893. 



