Antimony with Rubidium. 



279 



In polarized light these crystals show an 

 extinction parallel to the ortho-axis. With 

 crystals flattened parallel to the basal plane 

 an obtuse bisectrix may be seen nearly nor- 

 mal to the base. The plane of the optical 

 axis being at right angles to the symmetry 

 plane. 



RbCL2SbC\ . H % 0.— The crystallization 

 of this salt is monoclinic. Crystals were 

 made up to a length of about 9 or 10 mm . 

 The forms observed were : 



rig. 7. 



a, 100, i-l 

 c, 001, O 

 in, 110, 1 



d, 021, 2-i 



e, OIL, ~[-i 



p, 221, -2 

 x, 101, l-i 



The habit is shown in hV. 7. The axial ratio is a : b : c 1 



1 : 0-820 ^ = 001 a 100 89° 28£'. 



m~m, 110^110 

 a ^x, 100 a 101 

 m~a, 110 a 100 

 a aC, 100 ^ 001 

 x aC. 101 a 001 

 c *e, 001 a 0U 

 c A-d, 001 a 021 

 a A j), 100 a 221 

 p *d, 221 a 021 



Measured. 



*60° 57' 

 64 49 

 59 32 



*89 28£ 



*25 51+ 

 39 10 

 58 20 

 63 5 

 27 5 



Calculated. 



64° 40' 

 59 32 



39 21 



58 37 



63 6 



26 37 



The crystals flattened parallel to the ortho pinacoid, show in 

 polarized light an extinction parallel to the ortho-axis and in 

 convergent light a bisectrix and one of the ring systems appear 

 near the limits of the field. The plane of the optical axis is 

 the clino pinacoid. 



The 28 : 10 bromide is pseudo-hexagonal. Basal plates 

 always showed an intricate twinning when examined in polar- 

 ized light. The pyramidal faces were horizontally striated 

 and to such an extent that no satisfactory measurements could 

 be made. In every respect this compound resembles the 

 23 : 10 chloride described by Kemsen and Saunders. 



In conclusion the author wishes to express his indebtedness 

 to Prof. H. L. Wells for valuable advice in connection with 

 the present investigation and to Prof. S. L. Penfield under 

 whose generous supervision the crystallography of these salts 

 was investigated. 



Sheffield Scientific School, June, 1893. 



