( 360 ) 



A distinct flcavauc was nol fomid ; 1 lic svnimetrv must be deduced 

 from tlie development of the tbrnis, while etching experiments cai ried 

 out for the piii-j^ose of further confirmation did not give positive 

 results. 



The crystals are optically monaxial and do not exhibit cii-cular 

 polarisation. Refraclioii and double refraction are both strong ; the 

 latter is positive. 



Topical parameters : •/ : »f' : m = 6,1545 : 6 1545 : 4,8061. 



II. A^[M0NirM-SALT : (.V//J CO, CCh ■ HCO, CCJ,. 



The analysis gave: 4,927„ SH,: calculated: 4,947„. 



Sp. Gr. at 19° 1,775; molecular-volume = 193,80. 



Large octahedra, besides some smaller ones which are generally 

 flattened along two parallel planes ; the habit is that of the potassium- 

 salt. The crvstals are shown in Fig. 2. 



Ammonium-Salt. 

 Fig. 2. 



Tetragonal-trapezohedric, • 

 a:c = l: 0,7678. 



Forws observed: Only o = |lll|, large and very lustrous; in 

 the smaller crystals the planes were mostly dull and inflected, but 

 in the larger ones they gave very sharp reflexes. 



