275 



The geometrical as well as (lie optical properties, wHh the exception 

 of the peculiarity just mentioned, are in both cases perfectly agreeing. 

 There can be no doubt whatever as to the fact that the two optically 

 active salts crystallise in non-superposable mirror-images, although 

 the crystals themselves do not show a distinct rotatory power. 

 Stereographical projections of (he dextro- and laevogyrate crystal- 

 forms are given here in fig. 5^ and 5/;, for the purpose of surveying 

 the general zonal relations. 



ioio 



1010 



1100 0110 



0110 



1100 



a Fig. 5. h 



Stereographical Projection of the Crystal-forms of dextro- and laevo- Potassium-RhodiumOxalate. 



(+ 1 HoO). 



From these facts it becomes clearly evident that in the case 

 investigated Pasteur's principle appears fully confirmed. Indeed, a 

 non-superposable hemihedrism of the crystal-forms can be stated as 

 inseparably accompanying the enormously strong optical activity of 

 the solutions of these salts. However, it is worth attention that even 

 here this hemihedrism only manifests itself by the occurrence of a 

 single trigonal bipyramid, and never by the presence of any 

 "trapezohedral" face, as e.g. in the case of quartz; this fact again 

 may in some way or other be connected also with the lack of 

 chemical contrast between the dissymmetrically arranged substitutes. 



Finally it may be remarked that a solution of these salts after 

 three days, exposure to the light and even to the sun-light, did not 

 exhibit any appreciable photochemical decomposition. In aqueous 

 solution, however, the substance exposed in quai^tz-v essels to the 



