LATENT AND SPECIFIC HEAT. 333 



fication can take place, but it is possible to keep substances 

 in the liquid condition at lower temperatures. "Water 

 standing perfectly quiet sometimes cools several degrees 

 below the melting point without freezing, but, upon agita- 

 tion in any perceptible degree, solidification immediately 

 takes place. 



(a.) Persons who sleep in cold chambers sometimes notice, upon 

 arising, that as soon as they touch a pitcher of water that has been 

 standing in the room over night, the water quickly freezes. If a 

 particle of ice be dropped into the water the same result follows. 

 We may say that, in this condition, liquids have a tendency to freeze 

 which is kept in check only by the difficulty of making a beginning. 



524. Heat from Solidification. (1.) By surrounding, 

 with a freezing mixture, a small glass vessel containing water, and 

 a mercury thermometer, the temperature of the water may be re- 

 duced to 10 C. or 12 C. without freezing the water. A slight 

 movement of the thermometer in the water starts the freezing and 

 the temperature quickly rises to C. 



(2.) Place a thermometer in a glass vessel containing water at 

 30 C. and a second thermometer in a large bath of mercury at 10 C. 

 Immerse the glass vessel in the mercury. The temperature of the 

 water will gradually fall to 0C., when the water will begin to 

 freeze and its temperature become constant. In the meantime the 

 temperature of the mercury bath rises, and continues to do so icliile 

 the water is freezing. 



(3.) Dissolve two weights of Glauber's salt in one weight of hot 

 water, cover the solution with a thin layer of oil and allow to cool, 

 in perfect quiet, to the temperature of the room. By plunging a 

 thermometer into the still liquid substance, solidification (crystal- 

 lization) is started and the temperature rapidly rises. Dr. Arnott 

 found that this experiment was successful after keeping the solu- 

 tion in the liquid condition for five years. 



(4.) Mix equal quantities of dilute sulphuric acid and of a satu- 

 rated solution of calcium chloride (not chloride of lime), the two 

 liquids having been allowed time to acquire the temperature of the 

 room. The two liquids are converted into solid calcium sulphate, 

 with a marked increase of temperature. In this case, as in some 

 of the other cases, part of the heat observed is probably due to 

 chemical action, but more to the conversion of the latent heat of 

 the liquids. 



