Molecular Constitution of Water. 483 



8. The Melting of lee as a Phenomenon of Dissociation, 

 and the Higher Valency of Oxygen. 



The polymerization o£ hydrol, which we have been studying, 

 is only a special case of a general tendency o£ oxides, both 

 organic and metallic, and other oxygen- containing compounds, 

 to polymerize (see L. Henry, " The Polymerization of the 

 Metallic Oxides," Phil. Mag. [5] xx.). This tendency is best 

 explained by assigning to oxygen a higher valency than 

 the dyad which it usually shows. Evidence for the tetrad 

 nature of oxygen has been submitted by Friedel, Heyes 

 (Phil. Mag. [~5J xxv.), and Briihl (Ber. d. Deut. Chem. GeseL 

 xxviii., xxx.). The tetrad valency may in reality be hexad 

 sometimes ; but on the principle of assigning the minimum 

 valency that will explain the facts, we shall assume oxygen to 

 be tetrad. The graphic formula for trihydrol then becomes 

 that shown : — 



H H 



I I 



H-O- -O-H 



\ / 



\. / 



H H 



The centres of the three oxygen atoms determine a plane 

 and a triangle in it, whose average shape must be equilateral. 

 It is improbable that the hydrogen atoms lie in the same 

 plane as the oxygen, but as their masses are small in com- 

 parison with those of the oxygen, the centre of mass of each 

 H 2 group is near to the centre of the oxygen atom in it, and 

 the equilateral triangle must be the dominant feature of the 

 molecule of trihydrol. The hexagonal form of the ice crystals 

 and the formula of trihydrol both demonstrate that the domain 

 of a molecule of ice is an equilateral triangular prism. As 

 this is, I believe, the first case in which a definite shape has 

 been ascertained for a molecule, it would be interesting in 

 connexion with it to investigate systematically the properties 

 of crystalline ice in different directions. 



For dihydrol, on the same principle, the graphic formula 

 will be this : — 



H H 



6= =6 



I l 



H H 



There is a strong probability that in water some of the 



