57 



With respect to the syniiuetrj of the ci^stals the same can be 

 said as in tiie case of the dextrogyratory compound. Corrosion-expe- 

 riments on the faces jlOlj and |110{ by means of water, mixtures 

 of water and alcohol, etc. in most case gave irregularly detined 

 corrosion-ligures, which had the character of elevations. 



The crystals are uniaxial with negative birefringence ; like those 

 of the dextrogyratory component they show a strong circular pola- 

 risation in the direction of the optical axis, which for a plate of 

 about 1 mm. thickness appeared to be c(pial and directed oppositely 

 to that of the dextrogyratory crystals. 



On superposition of a dextro- and laevogyratory crystal, the latter 

 being the upper, the Airy -spirals are nicely seen, with their direction 

 of rotation Just opposite to that mentioned in the description of the 

 dextrogy ratory crystals. 



The specific gravity of the crystals was pycnometrically deter- 



,25° 

 mined and found to be o—— = 1.972; the molecular volume thus 

 4° 



is: 261.19, and the topical parameters are : / : if) ; cu = 



= 6.7589 : 5.6767. 



V. Racemic L uteo- 'rriethi/Icnediamine-Cobaltinitrate. 

 Formula : jCo (Aein),! (NO,), 



This compound was prepared by treatment of the racemic bromide 

 in aqueous solution with a warm solution of the quantity of silver- 

 nitrate calculated. The solution separated from the precipitated 

 silver-liromide was sufiliciently concentrated on the waterbath ; at 

 roomtemperature dark red or brownish red, big, hemimorphic 

 crystals will be separated. 



In general tiie parameiers and angular values appear to be the 

 same as previously published (Z. f. Kryst. 39. 548. (1904). The 

 figure reproduced there however must now be changed, because the 

 hemimorphy is now clearly demonstrated ; further a wrong value 

 of the angle o : q was introduced in the description, evidently by an 

 accidental interchange of the symbols j021j and il20j.') For the 

 purpose of comparison of the calculated parameters with those of 

 the optically active forms, we have, contrary to the common usage 

 the polar binary axis as the a-axis. 



') These inconect data are also reproduced in Ctroth's Cliemisclie Krystallographie, 

 11. 140. (1908) ; they must be corrected there by the numbers given here. 



