52 



Big crystals, occasionally a cc.m. in volume; tliev are hrowniish 

 red, in most cases thick |)risms witli beautifully develo|)ed, lustrous 

 faces. Commonly they are tlattenetl parallel to two o|)posite faces of 

 m ; also the dodecahedrical crystals were observed, which are described 

 in the case of the laevogyratory antipode. 



DitetragoiKil-hipyrmnidal. 



a : r> = 1 : 0.8399. 



(Jliserved Forms: in =z \l[{)\, in most cases predominant, sometimes 

 giving multiple images; o = {101 j, with great, lustrous faces, allowing 

 very accurate measurements; (oz=\20i\, well developed, but often 

 absent, (fig. 2a and 2/*). 



o XT' 



Angular Values : Measured: Calculated: 



„:'o =z=(101):(0n) = *54° 8.^ — 

 m:o =(101): (110)= G2 56 

 j/t:7/* = (110):(lT0)= 90 1 

 ,- : to=: (101): (201)= 18 59 

 to : »n = (201) : (110)= 52 36 



Dpxtrogyratory Triethylenediamine- 

 Gobaltibromide. 



A distinct cleavage could not be stated. 



On {llOj the extinction is normal; the crystals are not appreciably 

 dichroilic. They are uniaxial, with negative birefringence. They 

 show a strong rotatory polarisation: a j)late perpendicular to the 

 optical axis appeared to be strongly dextrogyratory : about 25° or 30" 

 for the transmitted orange-red light, and a thickne.ss of 1 m.m. If 

 a similarly directed plate of the laevogyratory salt is combined with 

 it, one sees the spirals of Airy very distinctly like four dark beams, 

 radiating from the centrum of the image into direction of motion of 

 the hands of a clock, if the dextrogyratory plate is the upper-one 

 of the two. 



The specific weight of the cryslrals was at 25° C. : f/4° ^ 1.97J ; 

 the molecular volume is thus : 26J .29, and the topical parameters are:, 

 X .- tl' ; <o — 6,7759 : 6,7759 : 5,6910. 



By means of a diluted solution of potassiumchlorate, finally corro- 



