5^ FREEZING OF WATER. 



forming, would then sink through the water to the 

 bottom, and thus soon cool the whole mass of water. 



65. This expansion of water in the act of freezing, 

 takes place with immense force, giving rise to the 

 bursting of water-pipes and vessels full of water, in 

 cold weather. It is often supposed that this eifect is 

 occasioned by the thaw, and not by the frost. This 

 is a mistake; the mischief is caused by expansion at 

 the moment of freezing, though we only discover it 

 on the approach of warm weather, when the ice begins 

 to melt. Another, and very important natural result 

 of this power, is the disintegration or breaking up of 

 rocks, stones, and soils by frost, during winter. A 

 few drops of water, in freezing, are able to break 

 asunder the hardest rocks, and this effect year after 

 year, gradually destroys them, causing them to crum- 

 ble down into powder (647). 



66. It has already been stated that water is not an 

 elementary or simple substance; it is a compound, 

 and consists of two gases. This fact at first seems 

 incomprehensible, for we can hardly believe it possi- 

 ble that a hard and solid substance like ice, or a 

 weighty fluid like water, is composed of colorless 

 and invisible gas. The difficulty, however, greatly 

 diminishes when we remember that heat alone, with- 

 out adding anything to the weight of ice, converts it 

 into water, and that a little more heat will convert 

 that water into an invisible colorless vapor; for, as 

 has already been said (43), pure hot steam is quite 

 invisible, and only becomes visible to us when partly 



