780 MAXIMUM DENSITY OF WATER. 



of water between 4 and amounts only to -goV^th of 

 its volume. 



That water at is lighter than water at 4 may be 

 easily demonstrated. Into a rather large glass of 

 water a quantity of pounded ice is thrown sufficient to 

 fill nearly the upper half of the glass, and two thermo- 

 meters are inserted into it, as shown in fig. 388, one 

 bulb being in the middle of the ice, the other reaching 

 to near the bottom of the vessel. 



The particles of water in contact with the ice are 

 cooled and sink down to the bottom of the vessel ; 

 the descent will last as long as the effect of the 

 cooling is to make some of the water heavier than 

 the remainder ; that is until the temperature of the 

 descending particles has fallen to 4. As the cooling 

 proceeds the particles become lighter, and remain on 

 the top ; consequently after the vessel has been left 

 undisturbed for some time the lower thermometer in- 

 dicates nearly 4 and the upper about 0. The reason 

 that the thermometers do not exactly remain constant 

 at 4 and respectively is, that the air surrounding 

 the vessel continually gives up heat to the vessel and 

 indirectly to the water. 



The experiment should be made in a cool room, as the warm air 

 around the vessel affects the temperature of the liquid very con- 

 siderably, and will cause so lively a circulation of particles within 

 the body of the liquid that the portions which differ in density 

 are scarcely ever distinctly separated. If the temperature of the 

 room is maintained at 2 the two thermometers will indicate exactly 

 or 4 respectively. Both thermometers must be supported in the 

 desired position by retort clamps. 



In the case of liquids we obviously cannot speak of 



