Peculiar Properties of Water 



93 



THE PECULIAR PROPERTIES OF WATER IN LIGHT OF 

 ITS MOLECULAR STRUCTURE. 



F. O. Anderegg, Purdue University. 



Water is such a common substance that we usually take it for 

 granted and it is seldom that we stop to consider the reason for its 

 peculiarity. Occasionally when we examine some of its physical and 

 chemical properties we are struck by their difference from similar 

 properties of numerous organic liquids. The old saying that "oil and 

 water will not mix" is based on actual fact and the reason lies in their 

 molecular structures. 





Fig. 1. The specific heat, compressibility and density of liquid water are plotted 

 against the temperature. The data are taken from the 4th ed. of Landolt and Boern- 

 stein. 



Water has the formula H2O and hence a molecular weight of 18 

 and yet it is a liquid at ordinary temperatures with a remarkably high 

 boiling point, and exceptionally high latent heat of vaporization. Its 

 large dielectric constant is coincident with its great solvent and ionizing 

 power for electrolytic compounds. It is, comparatively, a rather dense 

 liquid but its density reaches a maximum at 4° C. On cooling below 

 this temperature expansion takes place and finally, on freezing, a 

 further notable increase in volume occurs. Water is one of the very 

 few substances known, which expands on solidifying. A plausible ex- 

 planation will be given for this expansion. 



The specific heat of water is the largest of rny known substance; 

 it varies with the temperature but not regularly. A minimum is reached 

 between 20 and 25° (figure 1). The curve to the left of this point 



'Proc. Ind. Acad. Sci., vol. 33, 1923 (1924)." 



