14 Blake — Some Isomorphous Triple Thiocyanates. 



C\Ag^Ba(SGN)^. 



■The crystals of this salt have the habit shown in figure 1, 

 consisting of the prism, m{110), and the pyramid of opposite 

 order, ^(201), although the basal plane, c (001), only slightly 

 developed, is sometimes present. Its external form gives no 

 indication of its sphenoidal character. The following angles 

 were measured, the asterisk marking the fundamental meas- 

 urement: 



Measured. Calculated. 

 q^^q", 2.01/^201 122° 14'* 



q/^q\ 201/^021 76° 30' 76° 30' 



rriy^q, 110/s201 51° 45' 51° 45' 



Vertical axis c = 0-9063. 



Indices of refraction for sodium light : 



oj=l-7'761; e= 1-6788. Difference = 0-0973. 



Cs^Cu^Ba{SCN)^. 



The crystals of this salt sometimes have the same habit as 

 that of the silver-barium compound, figure 1, but usually they 

 are modified by the sphenoidal faces, p (HI), and the base, 

 c (001), as shown in figure 2. In one crop of crystals more 

 than twenty individuals were examined, and no variation was 

 observed in the distribution of the p faces, truncating the 

 alternate edges of the pyramid of the second order, q (201), 

 thus clearly establishing the sphenoidal character of the crys- 

 tallization. Another lot of crystals presented a very different, 

 almost cubical appearance, owing to the large development of 

 the basal plane, c^ figure 3, with the pyramid of the second 

 order ^, and the sphenoid, p, only slightly developed. Here, 

 a^ain, there was no variation in the distribution of the faces of 

 the sphenoid, p, replacing the alternate edges between c andm. 

 On one crystal a single but well-developed face of the prism of 

 the second order, a (100), was observed, this being the only 

 observation of this form on any of the salts of the series. The 

 following angles were measured : 



Measured. Calculated. 

 q/^q\ 201/^201 122° 52'* 



q/^q', 201/s,021 76° 44' 76° 47' 



ony^q, 110/v201 51° 38' 51° 37' 



C/^2h 001/^111 52° 23' 52° 24' 



Vertical axis g = 0-9183. 



Indices of refraction for sodium light : 



0)= 1-8013: e= 1-6882. Difference = O'l 131. 



