C. W. Cook— Crystal Form of Alkali Bolides. 143 



based upon maximum schimer aud may vary therefore from 

 the true value. 



Hydrated Sodium Bromide (NaBr, 2H Q 0). 



This compound was studied crystallographically by Mitscher- 

 lich* in 1829. He states that the crystals are stable below 

 30° C. The crystals obtained by the author, however, lost 

 their water of crystallization quite rapidly at the temperature 

 of the room, so that complete measurements were not possible. 

 Observations in the prism zone confirm the work of Mitscher- 

 lich, as may be seen from the following comparison : 



m : m'" = (110) : (110) = 61° 28' (Mitscherlich) 

 m : m'" = (110) : (110) = 61° 24' (Cook). 



In addition to the above, a new form, 6>jl20[, was observed, 

 which on account of the close agreement of the observed and 

 calculated angles may be considered as well established. The 

 angles are : 



Observed Calculated 



b : o = (010) : (120) = 40° 2' 40° 4' 



The prism faces were characterized by a pronounced skeletal 

 development. 



Hydrated Lithium Bromide (LiBr, 2H 2 ?). 



The hydrated lithium bromide is a very stable compound, 

 some of the crystals which have been kept for four years show- 

 ing but slight efflorescence. The crystals examined were 2*5 

 to 5 mm in length and well developed, the faces giving excellent 

 reflections. 



The compound crystallizes in the prismatic class of the 

 monoclinic system, the elements of crystallization being : 



a : b : e = 0-83665 : 1: 1*1188 (3 = 107° 18' 30" 



The crystals show in general a short prismatic or tabular 

 habit, two variations of this type of development being 

 observed. 



Type one, which may be characterized as basal tabular, is 

 represented in tig. 1. This type was assumed by four of the 

 five crystals measured, and possessed the following forms > 



ajlOO}, c{001|, m{110}, o|120{, x\l02\, p{0ll}. 



A pyramid in the zone (120) (001) was also observed, but the 

 reflections from it were so poor that no attempt is made to 



* Mitscherlich, E., Pogg. Ann., xvii, 385-388, 1829. 



