542 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



pheric pressure is on the basis of polymerization. The effect of de- 

 creasing temperature is to increase the polymerization. For the 

 present purpose we may think of the molecule stable at higher tem- 

 peratures as a single molecule and that at lower temperatures as a double 

 molecule, although the latter is more probably triple and the former 



PRESSURE. KGM/CM^ X 10".^ 



Figure 37. Shows the total change of volume of water between 0° and 

 22° as a function of the pressure. 



double. The double molecule must furthermore be thought of as 

 occupying more than twice the volume of each of the single molecules 

 of which it is composed. The effect of a decrease of temperature on 

 volume is twofold : a decrease such as takes place in any normal liquid, 

 and an increase due to the clustering of single molecules into double 

 ones. This increase becomes increasingly rapid at low temperatures 

 because of the increasingly rapid polymerization. At 4° it has become 

 sufficiently rapid to neutralize the natural decrease, and at lower tem- 

 peratures volume increases with falling temperature. The way in 

 which polymerization is affected by pressure can best be discussed after 

 reviewing the data below 0°. 



The data below 0° show still more strikingly than those above 0° 



