238 IOWA ACADEMY OF SCIENCE 



the tubes had been filled with both kinds of water and left stand- 

 ing, it was noticed that the tubes holding the unboiled tap water 

 had their walls covered with air bubbles while the others were 

 perfectly clear. This observation, along with observations 

 made on the drop of temperature, gave some very valuable in- 

 formation toward the explanation of the phenomenon. The 

 temperature drop was read by filling comparatively large tubes 

 with boiled and unboiled water at exactly the same temperature. 

 The temperature was approximately the same until at about 

 zero or a little lower where the unboiled water began to freeze. 

 The boiled water, however, continued to cool until from minus 

 two to minus five degrees centigrade, when it suddenly crystal- 

 lized into ice, while the temperature again rose to zero. 



This difference in freezing probably was due to the fact that 

 air particles, with their impurities, form nuclei where crystalliza- 

 tion into ice may set in. In the unboiled water crystallization 

 begins at zero, but in the boiled it is delayed while the water 

 cools to several degrees below zero. Then when it does set in, 

 the water freezes more rigidly into the tube, as the ice forms 

 just as soon in the center as on the outside, which is not the 

 case with unboiled water. This rigid freezing causes greater 

 pressure to be exerted on the walls of the tube, making it harder 

 for the ice to slide away. Then on further expansion of the ice, 

 the tube bursts. 



On studying the ice of both kinds of water it was noticed that 

 a white, cloudy core existed in the center. The core was much 

 smaller in the ice from the boiled water. On breaking these 

 tubes in two, this center was found to be slushy and honey- 

 combed, and the whole central portion of the tube filled with 

 air bubbles. Professor Quincke of the University of Heidelberg 

 (Proc. Roy. Soc. Canada 3, p. 24, 1909) explained the presence 

 of the air in the center by the fact that at the boundary line 

 between the ice and the water in a freezing solution a surface 

 1 ension exists which forces the air and salts away. It is pre- 

 cisely the same action that causes the ice of impure pond water 

 to be purer than the mother liquid. 



In studying the drop of temperature we noticed that the 

 boiled water froze just as solid in the center as on the outside 

 when freezing started. In the unboiled water, however, the ice 

 formed on the walls and slowly froze toward the center. Thus 

 in the very act of freezing a core would form in the center of 



