Wells and Penfield — Series of Caesium Trihalides. 23 



(i-2, 1120), fig. 7. Only that portion is perfect which is in- 

 cluded between the irregular dotted lines, the upper and 

 lower angles of the rhombohedrons ^ 



being truncated by irregular warped 

 surfaces. In their growth the indi- 

 viduals of a whole series of crystals, 

 with similar orientation, are piled 

 upon one another in the direction of 

 the vertical axis. The scales are 

 about 6 mm in diameter. 



The measurement which was taken 

 as fundamental is : 



r*r, over a, 1011 ^ 0111 = 99° 48' 



giving for the length of the vertical 



axis, c=0 96363. The following measurements were also made : 



a*.a=60° 0', 60° 1", 59° 59' Calculated 60 c 0' 

 a*f, 12I0a0221= 31° 45' " 37° 49' 



The remaining compounds containing no iodine, were much 

 more unstable than those previously described. By making 

 the measurements in a cold room very satisfactory results were 

 obtained, the crystals retaining enough luster to give good 

 reflections, even after they had suffered considerable decom- 

 position. 



CsBi\. — The forms observed on this salt are o, m and d. 

 The habit is short prismatic, with either m or d predominat- 

 ing, while b is usually wanting. Single crystals are sometimes 

 10 mm in length, but groups of small crystals are more apt to 

 occur. 



OsClBr 2 . — The only forms observed on this salt are m and c. 

 The habit is short and stout prismatic. Single crystals are 

 sometimes 15 mm in length. 



CsCl^Br. — The forms observed on this salt are c, m and d. 

 It crystallized in stout prisms, over 10 mm long, terminated like 



fig.i. 



Method of analysis. 



The samples were prepared for analysis by pressing on 

 paper. The drying was not always very good, both on account 

 of the haste sometimes necessary to avoid too much decompo- 

 sition, and on account of the great tendency of the crystals to 

 contain cavities filled with liquid. 



Caesium was invariably determined by weighing the normal 

 halide produced by heating. In some cases where the result- 

 ing normal halide was slightly contaminated by a higher 

 halogen, this was replaced by the proper one before weighing. 



