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SCIENCE PROGRESS 



A few years ago no explanation was ever offered, the for- 

 mula was written as above, or sometimes 



3K 9 C a 4 -2Cr 2 (C s 4 ) 3 -6H 9 0. 



which, if it expresses anything beyond the ultimate composition, 

 implies that the double salt is a loose aggregation of its three 

 components. This, which may or may not be true with 

 regard to the water of crystallisation, is certainly incorrect 

 and misleading with regard to the other constituents, for in 

 solution the salt does not show the characteristic behaviour 

 either of a chromium salt or of an oxalate, whilst on the other 

 hand it does give the characteristic reactions of a potassium 

 salt. 



With the advent of the electrolytic dissociation theory the 

 formula acquired the ionic form, K 3 +++ «Cr(C a 04) 3 ""~ indicating 

 in solution the presence of a negatively charged chromi-oxalate 

 ion. This is a distinct advance, but it leaves untouched the 

 question of the relationship of its parts. 



Werner's views on the constitution of such complexes first 

 suggested a structure, the consequences of which could be put 

 to the test of experiment. If, as seemed likely from its be- 

 haviour, the whole and not one-half of the oxalate residues were 

 united to chromium, the simplest arrangement would be 

 octahedral; if octahedral, the molecular configuration would 

 be enantiomorphous, if enantiomorphous two forms should be 

 separable and oppositely active. Experiment established the 

 correctness of these conclusions, and the constitution of 

 the complex ion can be regarded as settled in favour of the 

 following orientation in space of the oxalic chains : 



This marks a substantial advance, although two parts of the 

 problem still await solution, the constitutional as opposed to 



