76 PROCEEDINGS OF THE AMERICAN ACADEMY 



Crystalline Form of Antimonious Bromide. 



Orthorhombic System. 



Forms {100}, {010}, {101}, {110}, {HI (?)} 



Fig. 3, Plate I. 



a =1.224 b=l c= 1.064. 



Angles between normals. 



010 on 110 39° 14' 



Also, measured with microscope. 



The octahedral angles were calculated on the assumption that the 

 observed planes were those of" a fundamental octahedron ; but, although 

 the intersections with 110 appeared to be parallel, yet the edges were 

 too indefinite to give any certainty on this point. 



We also examined the crystals of antimonious bromide with the 

 polarizing microscope, and observed that one of the principal optical 

 sections was parallel to the prismatic edge, whether the light passed 

 normal to one or the other of the two pinacoids 010 and 100. * 



The specific gravity, in the solid state, of purified antimonious bro- 

 mide was taken in precisely the same way as that of antimonious 

 chloride : — 



* The only previous description of these crystals of which we have any 

 knowledge was giver by Nickles, " Coraptes Rendus," XLVIII. 837, in these 

 words : " Le broraure d'antimoine se presente en otaedres rhomboidaux, parfois 

 modifie's par des faces terminales ; ils constituent alors des prismes aplatis de 

 69 degres termine's par des pointements de 80 degre's ; Tangle de deux faces 

 contigue's de I'octaedre est de 181 degre's (les minutes ont dCi etre negligees le 

 cristal e'tant trop deliquescent)." In a later paper, "Journal de Pharmacie 

 et de Chimie " (3), XLI. 142, a figure is given, and this description is essentially 

 repeated, correcting the obvious misprint, 181 for 131 ; but, nevertheless, this 

 error has been very generally copied. The crystals measured by Nickles must 

 have had a very different habit from any we have seen, and we have not been 

 able to reconcile his description with our own observations. 



