Penjield — Crystallography of Ccesium- Mercury Halides. 317 



The crystals gave excellent reflections and only occasionally 

 a slight striatum interfered with making accurate measure- 

 ments. All of the forms were observed on two crystals and 

 probably others could have been found by measuring a larger 

 number. 



The crystals of CsHgClBr 2 have a similar habit, fig. 19, and 

 the distribution of all of the faces which gave distinct reflec- 

 tions is given in the spherical projection, fig. 20. This salt is 

 more insoluble than the chloride and the crystals are conse- 

 quently much smaller, not over l-| mm in greatest diameter. 

 All of the forms given above for the chloride were observed 

 except z and v, and in addition : 



d' 021, '2-z p"\ 111, '1 r", 131, 3-3, u', 111,, 7-7 t, 2l27, '^-8 



The crystals gave very good reflections, considering their 

 size, and the best measurements agreed so-well with those of' 

 the chloride that no attempt was made to calculate a new axial 

 ratio. The most marked difference in the two salts is the 

 development of the zone p" z" q" f y'" in the chloride and r" 

 d' t'" q'" p'" fm the chlorobromide. 



The measured and calculated angles are as follows : 









CsHgCl 3 



CsHg01Br 2 



Calculated. 



m' a/; 



110 a 



201 



44° 



45' 



45° 



6' 



44° 58*' 



/ ~p, 



201 a 



111 



26 



35 



26 



27 



26 34* 



p *v, 



111 A 



132 



18 



27 



18 



34 



18 27 



q ~d, 



132 ^ 



021 



18 



26 



18 



23 



18 27 



d a r, 



021a 



131 



26 



44 



26 



26 



26 34* 



x a r, 



1151 A 



131 



33 



40 



33 



20 



33 40* 



w a r, 



191 A 



131 



26 



36* 



26 



27 



26 33" 



u a r. 



171 A 



131 







21 



35 



21 47* 



r *p', 



131^ 



111 



26 



33 



26 



37 



26 34^ 



p' ~y, 



111 A 



111 



36 



m 



36 



37 



36 54 



b a r", 



010 a 



131 



44 



44 







44 58 



y'"~q'", 



795 a 



132 



22 



13 







22 13 



z" Ajp", 



197 a 



111 



28 



38 







28 35 



g"'* P :, 



132 a 



111 



50 



54 







50 49 



V"'*Q, 



795 a 



132 



62 



29* 



62 



22 



62 28-| 



p" * v, 



111a 



1131 



60 



46 







60 45 



P f *% 



111 A 



1131 



66 



53 







66 59 



f ~p'", 



201a 



111 







26 



38 



26 34* 



p'" a q'", 



111 A 



132 







18 



23 



18 27 



q'" a d', 



132 a 



021 







18 



34 



18 27 



f" a d', 



2127 a 



021 • 







10 



13 



10 19 



q a w. 



132 a 



191 



50 



59 



51 



4 



50 46 



q *p'", 



132 a 



111 







50 



50 



50 49 



q ~q'", 



132 a 



132 



60 



3 







60 4 



It will be seen from the spherical projection that the forms 

 of CsHgClBr 2 lie mostly in three zones, suggestive of hexag- 

 onal rhombphedral symmetry, although there is. nothing in 

 the arrangement of the faces, and still less with CsHgCl 3 , to 

 indicate that this is correct. The crystals of CsHgClBr, have 



