Thermal Expansion of Liquids

Liquids unlike solids can be poured. If a liquid is poured into a vessel, it takes the shape of the vessel. For this reason, a liquid cannot have linear and aerial expansivity, thus liquids have only volume expansivity. Liquids molecules have kinetic energy. This energy increases if the temperature of the liquid is raised Heating. Heating causes the molecules of liquid to move faster.

The instrument used to demonstrate anomalous expansion of water is called hope's apparatus. it consists of a brass cylinder, jacket J with a mixture of ice and salt and two thermometers A and B at regular intervals upward and at the bottom. The hope's experiment shows that water contracts as it cools down to 4 degree centigrade and then expands as it cooled further below 4 degree centigrade.

In the year 1805, the scientist T. C. Hope devised a simple arrangement, known as Hope's apparatus, to demonstrate the anomalous behavior of water

Hope's apparatus consists of a long cylindrical jar with two openings on the side, one near the top and the other near the bottom to fit thermometers in each of these openings. A metallic cylindrical air-tight trough with an outlet is also fitted onto the jar, on its central portion. Two thermometers are fitted air-tight in the two openings of the cylindrical jar. The thermometer near the bottom of the jar is $T_1$, and the one near the top of the jar is $T_2$. Now the cylindrical jar is filled with water

Water in lakes and ponds usually freezes in winter. Ice, being less dense floats on the water. This insulates the water below against heat loss to the cold air above. Water at 4 degree centigrade being most dense, remains at the bottom of the lake, while ice, being less dense than water floats on the layers of water. This enables aquatic animals to survive in the water below the ice.