48 



Wells, Wlutler and Penjield — Alkali- Metal 



Measured. 

 CaOT, 001 a 110 = *74° 26' 

 cp, 001 a 111 = *55 20 

 p~p, 111 aIII = *76 21 



Measured. Calculated, 

 CaS. 001 a 111 = 82° 12' 82° 15' 

 SaW, 111 a 110 = 23 20 23 19 

 p~m, 111 aIIO = 19 5 19 6 



With the polarizing microscope the plates show an extinc- 

 tion parallel to their diagonals. In convergent light nothing 

 of the ring system can be seen, but a dark bar crosses the 

 field in the direction of the symmetry plane, indicating that 

 the plane of the optical axes is the clino-pinacoid. 



The crystalline habits and axial ratios of CsCl.Cl 3 I and 

 RbCl.Cl 3 I are wholly different and all attempts to find any 

 similarity or mathematical relation between them has failed. 

 We have endeavored to detect any hidden relation that might 

 exist by examining separate crops of crystals, made from a 

 solution containing both salts. Each form alone and mixtures 

 of both were thus obtained, but no crystals of an intermediate 

 form could be produced. One unmixed crop, having the form 

 and angles of CsCl . C1 3 I, contained about sixteen per cent of 

 RbCl . C1 3 I, while another, having the form and angles of 

 RbCl . C1 3 I, contained about eleven per cent of CsCl. C1 3 I. 

 These results show that isomorphous mixtures can 

 be obtained of either form, depending upon which 

 salt predominates, while the absence of any inter- 

 mediate forms, and the inability to detect any mathe- 

 matical relation between the two kinds of crystals, 

 leads us to believe that the compounds are dimor- 

 phous. 



The form of KC1 . C1 3 I is monoclinic. This salt 

 was repeatedly made in line needle-like crystals, too 

 small to measure, by allowing a warm saturated solu- 

 tion to crystallize. By slow evaporation in a desic- 

 cator, at ordinary temperatures, stouter prismatic 

 crystals, over 20 mm long and 2 mm in diameter, were 

 obtained having the habit shown in fig. 6. These gave excel- 

 lent reflections and were measured without difficulty at winter 

 temperature. 



The forms which were observed are : 



f^\ 



100. 

 110, 



n, 120, i-% 

 d, 023. £-? 



The axial ratio is as follows : 



d : ~b : c = 0-9268 : 1 : 0-44725, ft 



100^001 = 84° 18' 



Measured. 

 m^m, 110 aIIO = *S5° 22' 

 d ~ d, 023 a 023 = *33 3 



Measured. Calculated 



AacZ, 100 a 023 = *84° 32' 

 Maw, 120 a 120= 56 58 56° 56' 



