( 366 ) 



Monoclino-prismatic . 



r/:6:C = 1,5515:1 : 3,3007. 



/?=87°48'. 



Forms observed: c = |001|, large, very lustrous and predominant ; 

 |101| and r = |1()1| about equally' stronglj' developed, and giving sharp 

 reflexes; ^^|011| reflecting very perfectly, broad and never want- 

 ing; ,5?=:{013|, very narrow and mostly absent ; to = |112j yielding 

 good reflexes; o^|112| even reflects better still. 



Angular vulues: Measured: Calculated: 



Indistinctly cleavable along |101|. 



On |001| the extinction is parallel and perpendicular to the 

 direction of the i6-axis; an axial image was not observed. 

 Topic parameters : x : ip : w = 5,2928 : 3,4115 : 11,2601. 



§ 5. From all these experiments may, therefore, be deduced the 

 remarkable fact, that the acid alkali-salts of trichloroacetic acid form 

 an isopolymorplious, and in all probability an iso^t'/ramorphous, series 

 with three monoclinic and one tetragonal-trapezohedric modification. 



It seems very peculiar that the two tirst terms of the series are 

 tetragonal and isomorphous ; that the /^/;-salt exhibits the second, the 

 Cy-salt the third and fourth possible form ; and that, — with a further 

 increase of the atomic weight, — the original optic monaxial form 

 of the T/-salt returns, but this time with an opposite optical character! 



The T/-salt is the nearest situated to the (iV^J-salt and is also 

 very adjacent to the 7v-salt. The two forms of the Rb- and Cs^-salt 

 exhibit — notwithstanding their great differences — an undeniable 

 analogy, while, fi'oni the analysis of the ihallous-tribroino-derivatiye, 

 it appears that tlie e\entual, more labile form of the thallous-salt, 

 occurring in mixed crystals, will probably be the nearest situated to 



