69 



A distinct cleavage was not observed. 



On jOOlj, JOIII and {lOJJ every where normal extinction. Tiie 

 crystals are not appreciably diciiroitic. The optical axial plane is 

 S100| ; the apparent a\ial angle is small, and the r-axis is first 

 bisectrix. 



The specific weight of the snl)stance at 25° C was found to he : 



25" 

 d „ =1.502; the molecular volume is: 275.26. 



4 



Topical pammeters: x : 'I' ■■ w = 6.1893 : 7.2867 : 6.1034. 



With tepid water on jOO I j beautiful corrosion-figures were obtained 

 after short treatment. They represented rectangular, pyramidal eleva- 

 tions, which were distinctly sijinmetrical with respect to the planes 

 |100| and \0\Q\. Consequently the crystals must be considered as 

 having hipyrainidal symmetry ; with mixtures of alcohol and water 

 rectangular, bilateral-symmetrical corrosion-figures w^ere also obtained, 

 which are in agreement with the holohedrical symmetry of the 

 rhombic system. 



XIII. Laevogyratory Luteo-Triethylenediamine-Cobalti-rhodanide. 



Formula : iCo(Aein),|(CNS),. 



Thick, short-prismatic, orange- or blood-red needles, which are 



very well built, and which give excellent images. Although the 



habit is difTerent from that of the dextrogyratory compound, the 

 crystaiform is evidently quite the same. 



Rhombic-bipyramidal. 



a:b:c = 0.8494 : 1 : 0.8375. 



Observed Forms: b = jOlOj, predominant and, like a = {lOOJ, 

 which is also well developed, giving excellent images; c = [001}, 

 small but very lustrous; .y ^ {201j and r^\i01\. rather large; 

 q:=[Oli\, somewhat larger yet, and like both foregoing forms, 

 reflecting excellently; in^\MO], about as broad as r, and reflecting 

 well; p = [VIO], narrow and a little duller; ö = jl21!, well deve- 

 loped; <u ^ |ril}, with small faces between o and r. The habit is 

 short-prismatic with respect to tiie c-axis, with predominance of 

 OlOj and {lOOJ. (Fig. 14). 



