699 



6280 A.Ü., considerably <j renter than those of the cohalti-sult; while 

 between 5640 and 6280 A.U. the reverse occurs, and the two salts 

 even show an opposite rotation as a consequence of the shift of 

 their maxiniuin and niinimuin; this shift is, in its turn, intimately 

 connected with the very different situation of the absorption-bands : 

 for the chromium-ssiU lias a very broad band in the orange, yellow, 

 partially in the green and the violet. It must, moreover, be remarked, 

 that our former experience has made it clear, that the triethijlene- 

 (Iiami?ie-c/u'omi-fia\l^ show in general only about half the rotations 

 of the triethylenediamine-cobahi-S£i\ts for corresponding wave-lengths. 

 From this it is evident how great and unexpected an influence the 

 presence of basic groups, or that of acid radicles, has, on the magni- 

 tude of the I'otation when they are dissymmetrically arranged round 

 the central metal-atoms of such complex salts. 



^ 3. As was already mentioned before, the racemic fO^^z/^Z-salt has 

 already been investigated by Copaux, who described it as a triclinic 

 substance, but not isomorphous with the corresponding rhodiwa-^&W. 

 As will be soon demonstrated, Copaux most probably obtained his 

 crystals from solutions evaporated in the darkness and at low tem- 

 peratures; for even in diffuse day-light the solution is decomposed 

 with development of carbondioxide and precipitation of cö^a/to-Otivi/a^ö, 

 — a decomposition which is quite analogous to the photochemical 

 decomposition of the corresponding /m'fc-salt. It must be remarked 

 that in this photochemical reaction, è/wé" light decomposes the solutions 

 much more rapidly, than red or yreen light, — in full agreement 

 with Draper's law. But it is a remarkable fact that y(?//6»i^ and öra?i(/<? 

 light, which is absorbed also to a considerable amount, has scarcely 

 any stronger influence than the only slightly active green or red rays. 



In our experiments the saturated solutions were evaporated in a 

 dark space, the temperature of which differed only slightly from 

 0° C. In this case we really obtained triclinic-pinacoidal crystals of 

 a dark green, almost black colour, and showing in most cases curved 

 faces and rudimentary forms; accurate measurements were therefore 

 very difficult. The angular values obtained really differ not inconsi- 

 derably from those published by Copaux, at least within some zones; 

 hut the identify of his crystals and ours need not be doubted in 

 any way, as may appear from the following values: 



Calculated: 



