( 367 ) 



that of the i^^-salt; the analogy with the second form of the G^-salt 

 is, however not so conspicuous. 



B}^ these relations it lias been clearly demonstrated how complicated 

 the family-relation of the crystal-building alkali-molecules is, and 

 how much the ex{)ected isomorphism may be confused by the occurrence 

 of |)o]ymorphism. 



§ 6. Efforts to find definite transition-points with the acid of the 

 crystallisation-microscope, were without result. On heating, an 

 apparent melting-phenomenon occurs in the crystals, to i)e attributed 

 to the fact that the split-off trichloroacetic-acid-molecule, causes the 

 occurrence of a liquid phase in the pores of the crystals, which then 

 become porcelain-like and opaque, while the}' are crossed with 

 innumerable cracks. On account of the decomposition of the substance, 

 it is not possible to prove the occurrence of another modification by 

 a thermic method. 



§ 7. Mixing -experiments. 



Although a more complete iiivestigation of the mixing-phenomena 

 of these salts must be postponed till later, still a few experiments 

 have been made, for a first orientation, which already have brought 

 to light some veiy peculiar phenomena. 



1. Thallium-, and Ammonium-salts. 



From mixtures of the thallous- and the ammonium-^ïiXi crystallise 

 small, well formed quadratic octahedra, afterwards larger ones of the 

 type of the (iVT/J-salt. The first crop of crystals are optically /w^vVm^. 

 In the last fractions there were found small crystal-clear, tetragonal 

 double-pyramids, which were faintly negative; the axial image was 

 normal. In the very last fractions there were found similar crystals, which 

 however, possessed a strongly negative double refraction. Their angular 

 values agree with those of the Tl- and the (iV//J-salt. There can 

 be no doubt as to the complete isomorphism of the two compounds; 

 probably, their mixing-series is an uninterrupted one. 



2. Potassium-, and Rubidium-salts. 



From mixtures of the potassium-, and the rubidium-salt are first 

 deposited crystals, which are quite analogous to those of the pure 

 7?6-salt. Later, small little plates appear with hexagonal limitations. 

 Measurements showed that they were well built, possess monoclinic 

 symmetry, and that their angles differ but little from those of the 

 Rb-üü^Xi. 



(001) : (Oil) = 72°35' (measured) (110) : ifO = 111°10' (measured) 



