is clearly visible : on JlOlOj lor vibrations parallel to the c-axis 

 orange-red, for those perpendicular to the former orange-yellow. The 

 specific weight of the crystals was determined at 25° C. pycno- 

 metrically : d^^ =1.845; the molecnlar volume') is thus: 577.8, 

 and the topical axes x :<« = 10,9400 : 7,4328. 



B. The substance pi-epared from piirpureo-dichloro-üüXi crystallised 

 from its aqueous solution in tiie shape of hexagonal plates, which 

 will commonly show not only r and iti, but also r and r'. The 

 optical behaviour and the angular values agree completely with 

 those of the previously described salt. Further, we obtained the same 

 moditications in separating the bromo-tartrate into its optically active 

 forms as in the first case; also tiie (/-bromo-tartrate was here identical 

 with that obtained from the first salt. There cannot be any doubt, 

 but tliat the two bromides aie (|iiilo identical; the specific gravity of 

 the last crystals also, being found at : 1.142 at 25° C, is in agreement 

 with tiiis supposition. 



With the kind assistance of my colleague Hau.-v a beautiful R(»nt(;kn- 

 ogram of these hexagonal plates was made. The stereographic 

 projection of it is reproduced on Plate I, in .4. It appears now, that 

 there is no ditrigonal symmetry at all: the photo reveals only a 

 single plane of symmelry, as if a mere monoclinic-doraatic symmetry 

 were present. For the present no other explanation can be given 

 here, than the supposition of the crystral being oidy a pseudotrigonal 

 complex of perhaps monoclinic lamellae; in every case the \ery 

 perfect approximation of that complex to a real ditrigonal crystal is 

 a (|uite remarkable fact ; if remains yet very strange however, why 

 only a single plane of synnnetry will appear in this image. 



II. DeMrogyratorij lAiU'o-Tr'trthtjIencuUaiinni'-Cohalübromith'. 

 Formula: [Co [Aeiii),\ Br, + 2 HJK 



The compound was obtained by the transformation of the racemic 

 salt in aqueous solution into the corresponding d-hroino-d-tartrdtj' 

 by means of silver-(/-tartrale and afterwards fractionated crystallisation. 

 The d-J)romo-d-tarti'nti' which is deposited first and whose beautiful 

 crystals are also desci'ibed in tiie following, is then treated with HBr 

 to convert it into the dextrogyratury bromide; the same happened 

 with the /-hroiiio-d-tartrate, which can be obtained only in the form 

 of a colloidal mass. The rotation of the two salts in aqueous solutions 

 appeared to be really equal but of opposite diiection. 



') In the following calculations we adopted 2M instead of M as the molecuhu- 

 weigfil of the racemic compounds. Tliis latter one is undoubtedly also present still 

 in the aqueous solutions of the salts. 



