PHYSICAL PARADOXES. 



extreme as to be practically one of a differ- 

 ent kind. The solidification of water in the 

 act of freezing is a case so extreme as to be 

 a process of a different nature from the previ- 

 ous contraction of the water under a tempera- 

 ture which, though falling, was still higher than 

 that at which it freezes. Freezing, in the case 

 of water, appears to be the formation of crystals 

 in which the molecules are arranged in rigid 

 formations at a greater distance from one 

 another than they occupy in the liquid. Thus 

 the ice occupies 10 per cent, more space than 

 the water out of which it was formed. 



It appears that, before the water is cold 

 enough for actual freezing, there sets in, at 

 about 4 C., a preliminary process in which the 

 molecules are already tending, with a force 

 continually increasing as the temperature falls, 

 to arrange themselves in the new formations 

 which require more room. Consequently, the 

 water expands progressively as it cools from 

 4 C. to o C., and then at the latter tempera- 

 ture undergoes a much greater expansion in 

 freezing. 



Thus we get the very curious and paradoxical 

 result that, starting with the water at 4 C., 

 or 39 F., and its level at B in the tube of our 

 flask (Fig. 30), it will not matter whether we 

 heat the water or cool it ; in either case it will 

 expand, and the column in the tube will rise 

 towards A. 



130 



