OxoNiuM Compounds. — By D. McIntosh, M. A., D. Sc, 



Dalhousie University, Halifax, N. S. 



(Read by title 14 May, 1924) 



Two contributions to theoretical chemistry have stimulated 

 greatly the interest taken in molecular ^ compounds. First, 

 the views of Werner, expressed at length in his "Neuere Ans- 

 chaungen auf den Gebiete der anorganischen Chemie," and the 

 electron theory of valence (Thomson, Lewis and Langmuir). 

 Amongst the compounds formed by the union of two well 

 defined molecules, the oxonium group has undergone numerous 

 investigations. Friedel, Collie and Tickle, and Baeyer and 

 Williger have contributed to our knowledge of these complexes, 

 and have shown that the ordinary view of the valency of oxygen 

 as two must be modified, and that this number must be increased 

 on occasions to four or even to six. This conception of quadri- 

 valent oxygen, common to chemistry for the last twenty years, 

 has been amplified by the electron theory of valency, so that 

 many compounds whose constitutions were previously obscure, 

 can now be represented graphically with, at least, some small 

 degree of probability. 



It appears that a little light is thrown on the mechanism 

 of solution, catalysis, substitution and ionization by a study 

 of these intermediate compounds. We stressed twenty years 

 ago the view that in many instances ionization is preceded by 

 chemical combination^ a view which now has many adherents. 

 Combination in solution is often indicated by the failure of 

 Raoult's law, and is not infrequently a partial explanation for 

 an apparent anomaly. For instance, water is insoluble in ether 

 and in hydrobromic acid at low temperature, but is 

 easily soluble in a mixture of the two, and from this 

 solution a compound' of the three components can be isolated. 

 Acetic acid forms no compound with alcohol, and the 

 production of an ester takes place very slowly. But a 

 compound is formed from alcohol, acetic and hydrobromic 



1. See Pfeiffer. Organische Molekliiverbindungen. The only serious 

 omission noticed in this book is that of the excellent and comprehensive work 

 of G. Baume. 



