Chemistry. — "The Sijxtem Sulphur Trioxide" I. By Prof. A. Smits. 

 (Communicated by Prof. P. Zeeman). 



(Communicated at the meeting of March '24, 1923). 



For some years the examination of snlplmr trioxide has been on 

 my programme, because I surmised that this substance would yield 

 suitable material to test the theory of allotropy. As, however, other 

 investigations had to go first, this examination could not be taken 

 in hand until a sliort time ago. 



In the meantime Berthoud ') Le Bi,anc with ROti.e ") published 

 each a treatise on vapour tensions and melting-points of this sub- 

 stance. Though these two papers will be discussed more at length 

 later on, I will make here already a few remarks, and more parti- 

 cularly in connection with the latter publication. 



The results published there prove with I he greatest clearness 

 that SO, is really a substance which not only can be used as a test 

 of the above-mentioned theory, but which is so eminently fit for it 

 that in this respect it is unequalled by any other. For the results 

 obtained show that both the liquid and the solid phases of the SO, 

 can behave as phases of more than one component, which without 

 any doubt must be attributed to the complexity of this phase. 



This complexity is owing to the occurrence of different kinds of 

 molecules in the same phase, which molecular-species are in 

 internal equilibrium with each other in the case of unary behaviour. 

 I emphatically pointed out on an earlier occasion that the term 

 "different kinds of molecules" should be taken in as wide a sense 

 as possible '). By them we should understand not only the isomer 

 and the polymer molecules, but also the electrically charged disso- 

 ciation products, ions -j- electrons, and it is self-evident, that in 

 many cases the dilference between molecular-species mentioned 

 here lies in a difïerence between the atoms. It is in particular the 

 more recent views on the atomic structure, that bring to light, that 

 there are very subtle differences possible between the different atoms, 

 which e.g. are in connection with a change of the quanta-values of 

 the valency-electron- paths, and this leads to kinds of molecules with 



') Helvetica Chem. Acta 5, 513 (1922). 



«) Ber. d. Sachs Akad. v. Wiss. Leipzig 74, 106 (1922). 



') The theory of Allotropy p. 2. 



