Manchester Memoirs, Vol. xlviii. (1904), No. 14. 7 



can we say that the groups 



X-0-KandX-0 = NH, 

 would not belong to isomorphous salts ? 



Lothar Meyer says {Outlines of Theoretical Chemistry) 

 " it has been assumed that an atom of potassium can be 

 " isomorphously replaced by the ' compound radical ' 

 " ammonium, composed of one atom of nitrogen and four 

 " atoms of hydrogen ; but if this is possible in one case, 

 " it may frequently happen that several atoms replace one 

 " single atom. If we admit this, then the whole foundation 

 ^' of these considerations (i.e. on isomorphism) is weakened" 

 (the italics are mine). We must also not forget that the 

 nitrates, the bichromates, and the persulphates of potas- 

 sium and ammonium are not isomorphous. There is thus 

 no argument from the theory of isomorphism which 

 negatives my view. 



The constitution of the metal-ammonium compounds 

 is sufficiently indicated by the formulae 



H3N = ClAg, H3N = ClCu, H3N = ClPtCl = NH3 



for the compounds of ammonia with the chlorides of 

 silver, copper, and platinum respectively. 



The correctness of this theory is rendered the more 

 probable by the ease with which it explains the existence 

 of the isomeric quaternary ammonium salts to which 

 reference has already been made. The stereochemical 

 configuration of ammonium chloride and its substitution 

 products, according to the usual ammonium theory, pre- 

 sents a special difficulty, owing to the fact that no 

 symmetrical solid geometrical figure with five corners 

 exists. In order, therefore, to arrive at a space formula, 

 it became necessary to assume that certain valencies 

 attached to the nitrogen atom are arranged in special 

 directions. This is obviously a very grave assumption, 



