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XL VI. The Molecular Constitution of Water. 

 By William Sutherland*. 



THE two chief irregularities in the physics of water,, 

 namely, its temperature of maximum density near the 

 solidifying point, and its great expansion on solidification, 

 seem to have long ago suggested the idea that water is a 

 mixture of two substances, whose proportions vary with the 

 temperature. In 1892 Rontgen (Wied. Ann. xlv.) in an 

 elegant but brief paper, showed that qualitatively all the pro- 

 minent exceptional properties of water could be accounted for 

 by considering water at different pressures and temperatures 

 to be a saturated solution of ice in some other form of H 2 0. 

 It seemed to me that sufficient data were in existence to' 

 enable one to work out quantitatively the actual constitution 

 of water; and I propose to show that steam being H 2 0, ice is 

 pure (H 2 0) 3 and water a mixture of (H 2 0) 3 and (H 2 0) 2 in 

 proportions whose dependence on temperature can be ex- 

 pressed by a simple formula. As H 2 is very generally used 

 as a symbol for water, and as hydrogen oxide is a long name 

 for so important a chemical species as H 2 0, I propose for 

 international convenience to call H 2 hydrol, (H 2 0) 2 dihydrol, 

 and (H 2 0) 3 trihydrol. Steam is hydrol, ice is trihydrol, and 

 water a mixture of dihydrol and trihydrol. The investigation 

 will be taken in the following order: — 



1. Constitution of water from its thermal expansion. 



2. Confirmation from optical refraction. 



8. Compressibility of water and dissociation of trihydrol 

 into dihydrol by pressure. 



4. Surface-tension and constitution of water in surface- 

 film. 



5. Latent heat of fusion, specific heat, and latent heat of 

 evaporation. 



6. The viscosity of water. 



7. Dielectric capacity. 



8. The melting of ice as a phenomenon of dissociation, and 

 the higher valency of oxygen . 



9. Summary of results. 



1. Constitution of Water from its Thermal Expansion. 



The starting point in this section is Mendeleeff's empirical 



approximate formula for the thermal expansion of liquids 



between 0° C. and their boiling-points, namely, p = p (l — kt), 



which, expressed graphically, as in the figure, with t for 



* Communicated by the Author. 



