Heat as a Quantity 167 



will be noted till after all the water in the smaller 

 beaker has become ice. By examining the beaker 

 at intervals, the time taken to -bring about the change 

 of the water at into ice at 0, may be approximately 

 found. It will be noticed that it is about four times 

 as long as was required to lower the temperature of 

 the water from 20 to 0. If the inner beaker be left 

 in the mixture for a further interval, it will be noted 

 that the ice will continue to give up heat to the cold 

 mixture of ice and salt, as shown by its temperature 

 faUing below 0. 



In the above experiment, the heat given out by 

 the water in cooling causes some of the ice in the outer 

 vessel to melt, and we have evidence that this heat is 

 actually given out in the fall of temperature experi- 

 enced by the water. The water, in changing to ice, 

 continues to give out heat its latent heat and melts 

 more of the surrounding ice, but we have no evidence 

 of this registered by the thermometer. That the 

 supply of heat from the inner to the outer vessel 

 is a continuous process, and does not stop when the 

 water reaches 0, may be inferred from the fact that 

 as soon as the whole of the liquid has become solid, 

 further decrease in its temperature is recorded by the 

 thermometer. 



108. EXPERIMENT 56. Into a porcelain evapor- 

 ating dish pour 20 c.c. of water, and take its tempera- 

 ture. Heat the dish over a small flame and note the 

 time taken to raise the temperature of the water to 

 100. Continue the heating with the same flame until 

 the water has been completely turned into steam. 

 Make a note of the time required to effect this change, 

 and take the temperature of the water from time to 

 time while it is proceeding. 



