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SCIENCE PROGRESS 



necessary to represent the ionisable atoms or groups as falling, 

 when the compounds assume the solid state, into positions 

 outside this complex, the particular positions taken up being 

 determined by the residual affinity of the whole group — that is, 

 by the resultant of all the chemical forces engaged. If it be 

 granted that the six atoms or groups in the inner zone occupy 

 the space round the central atom so fully that they are not 

 able to exchange their positions without leaving the inner 

 sphere of attraction, this octahedral representation leads to 

 various conclusions relating to the possibility of isomerism. 



For example, when the six groups are the same as in [MeA«] 

 or contain a single other group as in [MeA 6 B] the resulting com- 

 pounds should exist in one form only, whilst those having the 

 composition [MeA^Ba] should exist in cis- and trans-isomeric 

 series, having configurations which may be represented thus : 



B B 



m 



T 



This deduction has been confirmed in the case of compounds 

 of the elements platinum, cobalt and chromium; e.g. the com- 

 pounds [(N0 2 )»Co(NH 3 ) 4 ]X exist in two isomeric series. 



Again, in certain cases the theory predicts the existence of 

 optical isomerism; for example, if the groups B C and D are 

 situated relatively to the central atom in the positions of the 

 angles of one face of the octahedron (for example, the corners 

 i, 3, 4 of Fig. i) compounds containing complex radicles of the 

 form [MeA 3 BCD] should give pairs of optically opposed 

 isomerides of the configuration 



and again in compounds containing complexes of the composi- 

 tion 



[MeABQD,), [MeABCD 9 E]. and [MeABCDEF] 



