ARTICLES 257 



tion of the oppositely active complexes being in every case 

 possible owing to the widely differing solubility of the pairs 

 of compounds thus produced. 



Various acids and bases were employed, laborious investi- 

 gations having to be undertaken in each case to decide upon 

 the most suitable. 



The simplest example of the first type is found in triethylene 

 diamine cobaltic chloride : 



[Co(NH 2 -CH 2 -CH 2 -NH 3 ) 3 ]Cl 8 or <»(Co en 3 ]Cl 3 , 



which is made by leading a stream of air for many hours 

 through a solution of cobaltous chloride containing an excess 

 of ethylene diamine. The resolution of this compound, which 

 may be given as an example, was effected by adding to it two- 

 thirds of the equivalent amount of silver tartrate. On allow- 



ing the chloride tartrate rCoen 3 |^TTQ thus formed to 



crystallise d-triethylene diamine cobaltic chloride tartrate 

 separated. The laevo modification was obtained from the 

 mother liquor. These active chloride tartrates were converted 

 into the bromides of the active bases 



d]Co en 3 ] Br 3 and l[Co en 8 ] Br 3 



by treating them with a concentrated solution of hydro- 

 bromic acid. 



Triethylene diamine chromic chloride (Cr en 3 ] Cl 3 and 

 triethylene diamine rhodium chloride (Rh en 3 ]Cl 3 were simi- 

 larly resolved, and recently a compound of platinum [Pt en 3 ]X 4 

 has been added to the list. 



The fact that the optical activity of these compounds de- 

 pends neither upon the nature nor the valency of the central 

 atom nor upon the ethylene diamine, but upon the enantio- 

 morphous configuration of the molecule, was established by a 

 similar resolution of the tri-a-a-dipyridyl ferro-compounds 



[Fe Dipyr 3 ]X 3 , in which the base aa dipyridyl is com- 



N N 

 bined with ferrous iron. 



Many examples of the second type containing two molecules 



1 The symbol en =■ NH» " CH a ■ CH2 ' NH a , is used to simplify the formulae. 



