312 



TEMPERA TUBE. 



reaches 4 C., Us temperature of greatest density. 

 Heated, above this point it expands. 



(a.) Through the cork of a large flask pass a fine glass tube. Fill 

 the flask with water at the ordinary temperature, and insert the 



cork and tube so that the water 

 shall rise some distance in the 

 tube. Place the flask in a freezing 

 mixture, such as salt and pounded 

 ice. The water column in the 

 tube falls, showing that the water 

 is contracting. But before the 

 water freezes the contraction 

 ceases, the column in the tube 

 becomes stationary, and then be- 

 gins to rise again. This shows 

 that water does not contract on 

 being cooled below a certain tem- 

 perature, and that there is a tem- 

 perature of maximum density 

 above the freezing point. 



(&.) Fig. 242 represents a glass 

 cylinder with two thermometers 

 inserted in the side, near the top 

 and bottom, at A and B. Midway 

 between A and B is an envelope O, which may be filled with a 

 freezing mixture. The envelope being empty, the cylinder is filled 

 with water at C., and placed in a room at the ordinary temper- 

 ature, about 15C. As the water molecules at the side of the 

 cylinder become warm, they fall, and B soon records a temperature 

 of 4 0., while A remains at 0. This shows that the warm water 

 falls to the bottom. It falls because it is denser. It is denser 

 because it has been contracted by heat. 



If the experiment be varied by filling the cylinder with water at 

 the ordinary temperature, and C with a freezing mixture, the tem- 

 perature at B will fall rapidly, while it falls slowly at A. This 

 will continue until A reaches 4 C., when A begins to fall more 

 rapidly, and continues to do so until it reaches 0. These experi- 

 ments show that water is heavier at 4C. than at any temperature 

 above or below. 



489. Results of this Exception. This prop- 

 erty of water is of great importance. Were it otherwise, 



FIG. 242. 



