1865.] On the forms of some Compounds of Thallium. 



555 



II. "On the forms of some Compounds of Thallium." By W. H. 

 MILLER, M.A., For. Sec. R.S., Professor of Mineralogy in the 

 University of Cambridge. Received December 13, 1865. 



Nitrate of Thallium. 

 Prismatic, 1 0, 1 1=38 8'-l ; 1 00, 1 1 = 62 56'-3. 



Fig. 1 



Observed combinations : 1 0, 1 1 1 ; 1 0, 1 1 1, 2 1 1 ; 1 0, 1 I, 

 111, 211; 100, 110, 210, 111, 211; 100, Oil, 110, 210, 

 1 1 1, 2 1 1. 



No cleavage observable. 



From tbe observed minimum deviation of the brightest part of the 

 solar spectrum formed by refraction through the faces 100, 110, it 

 appears that the index of refraction of a ray in the plane 001, and 

 polarized in that plane, is about 1-817. The refrangibility of the 

 other ray is greater, its minimum deviation through the same faces 

 being 93 nearly. 



Sulphocyanide of Thallium. 



Pyramidal, 1, 1 1 =38 20'-3. 

 Observed forms : 1 0, 1 1 0, 1 1 . 



2T 



