WHY HOT WATER PIPES BURST 239 



tiie unboiled water which would not appear so easily in the 

 boiled water. Then the occluded air, as explained above, is forced 

 into this core of the unboiled water. Thus, when the ice freezes 

 toward the center, enough of this central mixture of ice and 

 water is forced away to take up the expansion of the ice. This 

 was proven experimentally. Eleven pairs of tubes were filled 

 alternately with boiled and unboiled water and frozen, and the 

 eleven tubes having the greatest expansion out of the top were 

 noted. Ten of them contained ice of unboiled water, and one of 

 boiled water. In the plumbing system, this slushy center, in- 

 stead of forcing the column of ice away as in the test tubes, is 

 itself forced toward the terminals of the exposed pipe. 



Thus we may say that boiled water freezes nearer to the na- 

 tural conditions than the unboiled. In other words, the un- 

 boiled water would freeze just as quickly as the boiled water if 

 it were air free, or vice versa, the boiled water would freeze 

 like the unboiled if it contained air. The latter was proven ex- 

 perimentally. Twelve tubes were taken, six filled with unboiled 

 water and six filled with boiled water that had been saturated 

 with air. The tubes burst approximately at the same time, as 

 was anticipated. 



The air in the freezing of the liquid, as we saw before, sep- 

 arates out and forms little white spots in the ice. This weakens 

 the ice and makes it more mobile, more easily forced away, 

 when pressure, due to further expansion, is exercised upon it, 

 than if it were solid. K. R. Koch (Ann. d. Phys. 41, pp. 709- 

 727, 1913) found the ice containing air bubbles to have a lower 

 elasticity than air-free ice. In other words, air weakens the 

 ice. This weak ice has a lower perpendicular pressure on the 

 walls of the tubes, and, therefore, the probability of the tubes 

 bursting is lessened. 



The air in the water also acts as a compressible medium, that 

 is, when the ice expands by freezing, the air is compressed to 

 make room for the expansion of the ice. 



Finally to prove that chemical reaction was negligible, boiled 

 and unboiled distilled water, which is practically free from 

 chemical impurities, was set to freeze. Adeney (Phil. Mag. pp. 

 361, 9, 1905) found that water absorbs air. The boiled water 

 broke the tubes first, as expected. Then the boiled, distilled 

 water was saturated with air and set out together with unboiled 

 water to freeze. The boiled water broke the tubes first. 



