700 



The specific gravity of these crystals, wliich commonly only showed 

 the combination-forms: m = \l\% ft = |irO|, c = |OOJi, q = \On\, 

 w = {Tl2j, and ^< = [lOOj and /> = lOlOj very narrow, — was at 

 15° C. determined at: ^/4o = 1,877; the molecnlar volume is there- 

 fore: 268,14. 



An analogy of form with the corresponding ?'Ao<:/m??i-, and mV/mm- 

 salts is not present; neither is this the case with the monoclinic 

 c/iromiufii-ssiU, which possesses 3 H,(). ^). 



These facts prove in every case undeniably, that at temperatures 

 in the neighbourhood of 0° C, the saturated solutions deposit 

 crystals of the racemic compound. But the stranger therefore appeared 

 to us originally the behaviour of solutions evaporating at room- 

 temperature. For from an also inactive solution, which during the 

 summermonths was slowly evaporated in a dark room at tempera- 

 tures only slightly differing from 18° C, dark green, almost black 

 needles were obtained, which even on superficial examination 

 appeared to differ appreciably from the triclinic racemate. Crystal- 

 measurements taught us, that they had trigonal symmetry, and that 

 their form was identical with that of the laevogyratory antipode. 

 A crop of small crystals of this cryslallisation-product, dissolved in 

 water, did however not show any appreciable rotation. Suspicion 

 immediately arose, that the racemic salt might have been split under 

 these circumstances into its antipodes spontaneously, and that no 

 trace of rotation could be detected according to our way of 

 investigation, only because the solution deposes the crystals of the two 

 antipodes besides each other in about equal number, so that a crop of 

 several crystals, which by the lack of hemihedral faces cannot be 

 discerned from each other, contains in general almost an equal 

 number of dextro- and laevogyratory individuals, when collected 

 from the solution at random. It is evident that such a mixture will 

 not exhibit any appreciable optical activity. If this suspicion were 

 true, the optical activity must appear immediately, if only a single 

 crystal at the same time were dissolved. Indeed, experience proved, 



J) The parametres of the cobalii-ssiM are: t/ : ö : c = 0,5963 : 1 : 0,6590 ; 

 a = 91°42'; /3=:101°23'; 7 = 88°22'. The chromiumsah is monoclinic, with: 

 a: 6 :c = 1,0060: 1 : 1,3989; /? = 86°0'. For the rhodium- 3ind iridium-szhs, d. 

 these Proceedings, 20, p. 270, (1917); and 21, 214, (1918). 



