249 



Angles : 



Cleavage parallel to c and m. 



On jllOj the extinction-angle is small, only 5° — 10° with respect 

 to the edge m-.in. The plane of the optical axes is |010|. 



^ 6. Laevogyrate Tki-etlyt,enediamine-rhodiüm-bromide. 

 \Rho{Eme),\Br, -{-2R^0. 



The substance was prepared from pure laevogyrate iodide by 

 heating its solution with freshly precipitated silver-bromide. After 

 filtration the solution was concentrated on the water-bath, and 

 crystallised at room-temperature. Very big, hexagonal thick plates 

 are deposited from the colourless solution, which are strongly 

 refracting and give extremely sharp reflexes. 



Ditetragoncd, apparently 

 hipyvamidal, and completely 

 isomorphous with the corre- 

 sponding cobalti-^'óM. 



a.c = ^: 0,8330. 



m 



tfi 



Forms observed: m ^ jllOj, 

 ordinarily with two predominant 

 parallel faces, very lustrous, but 

 often uneven ; o = |10i|, splen- 

 didly reflecting and with well- 

 developed faces. The shape of 

 the crystals is that of thick plates parallel to faces of the prism ; 

 elongation parallel to the c-axis. No indication of hemihedrism ivas 

 observed in any case, just as was stated in the case of the corre- 

 sponding cobalii-SR,\ts. 



Fig. 5. 



Laevogyrate Triethylene-diamine- 



Rhodium-Bromide. 



Angles: 



Calculated: 



o:o =(101): 

 o:m = (I01) 

 m:m=(110) 



63°5V2' 

 90 



Observed: 

 :(011)=*53°49' 

 :(110)= 63 5V-. 

 :(n0)= 90 



No distinct cleavability was observed. 



The crystals are optically uniaxial ; a plate perpendicular to the 



17 

 Proceedings Royal Acad. Amsterdam. Vol. XX. 



