The unusual expansion of water
Some substances do not always expand when heated. Over certain temperature ranges they contract. Water is an outstanding example. If we start with some ice at -10 °C and supply it with heat, it expands just like 0any other solid until it reaches 0 DC. After this it begins to melt while the temperature remains constant at 0 “C. This melting is accompanied by a contraction in volume of about 8 per cent. Between 0 and 4 “C the water contracts still further, reaching its minimum volume at about 4 “C. This means that water has a maximum density at 4°C. Beyond 4 °C the water expands. This behaviour is described as anomalous (= irregular).
The changes in the water volume between 0 and 15°C are shown graphically in Fig. 15.13. Unfortunately, on the scale of this graph, we cannot show the contraction in volume when ice melts, since this is nearly 700 times greater than the contraction of water between 0 and 4 “C. Incidentally, the contraction in volume when ice melts is matched by a corresponding expansion when water freezes to form ice. This explains why pipes sometimes burst during frosty weather though the damage does not become apparent until a thaw sets in.