The Expansion of Water -Demonstration. - Fill the bulb A, Fig: 1, with water at 4° C., up to the zero mark on B, at which point the volume of the bulb is 100 c.c. Close C and warm the water in the beaker to the temperature t° C.

Both the glass and the water expand, but the expansion of the water being much greater than the expansion of the glass, it rises in the calibrated tube. The amount of the expansion

at to in cubic centimeters, divided by the product of 100 c.c.  (t - 4) will give the average apparent expansion of water in glass per degree for the range of temperature tested.

The temperature 4° is taken as a basis in the determination of the apparent expansion of water, because at that temperature water has its smallest volume and maximum density. The liquid water expands not only when its temperature is raised above 4°, but also when its temperature is lowered below 4°. In the latter, which is known as its anomalous expansion, water differs from other liquids. When winter approaches, the water of ponds and lakes becomes colder at the surface and sinks, setting up convection currents, so that, before the water at the surface becomes colder than 4°, the entire body of water is of the uniform temperature of 4°. Were it not for the anomalous expansion of water, this process

 would continue down to the freezing point. This expansion, however, stops the convection currents, and when freezing begins, the water quite near the top is the only part that is colder than 4°, hence fish that are under the ice are in water of an almost uniform temperature.

Since the change in volume per degree is very small, it is best shown by a curve in which the scale of volumes is taken very large. In Fig. 2 each division in the vertical scale represents 0.00005 of the volume at 4°.

The expansion of water is not uniformly proportional to the temperature. As we go from 4° in either direction, the amount of expansion per degree constantly increases. From 4° to 5° the expansion is 0.000008 of the volume at 4°; from 14° to 15°,0.000146; from 24° to 25°, 0.000253. Liquids in general have different rates of expansion at different temperatures; in this they differ from solids and gases, which expand uniformly.

The rate of expansion of mercury, however, is nearly uniform. Its coefficient of cubical expansion, for temperatures near zero, is 0.0001818.

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مواضيع ذات صلة

The Spheroidal State

The Reflection of Radiant Heat

Selective Absorption

Radiating and Absorbing Powers

The Law of Charles

Boiling

Critical Temperature

Effects of Expansion in Solids

Absolute Zero

Condensation of Vapors; Distillation

Cubical Expansion

Effects of Expansion in the Air