Heat as a Quantity 



169 



Fig. 61. 



EXPERIMENT 57. Arrange two beakers as shown 

 in Fig. 51. The space between 

 the vessels is loosely packed with 

 cotton-wool. (The reason for 

 this precaution will be under- 

 stood after reading the chapter 

 on methods of transmission of 

 heat.) Weigh the inner beaker, 

 and introduce into it enough 

 water to fill it about half full. 

 Weigh the beaker and water. 

 Place a thermometer in the water and find its tempera- 

 ture. By gentle heating, raise its temperature about 5. 

 Replace it inside the larger beaker, keeping the ther- 

 mometer in its place while doing so. Wipe a small 

 lump of ice with a duster, note the exact temperature 

 recorded by the thermometer, and quickly drop in the 

 lump of dried ice. Stir well with the thermometer 

 until the ice is almost entirely melted. Note the 

 temperature. If it has fallen about 10, continue 

 stirring until the ice has all melted, carefully noting 

 the lowest temperature registered. If the decrease is 

 less than 10, put in another piece of dry ice, and 

 repeat this till the amount of ice added is sufficient 

 to cause the temperature to fall about 10. Make 

 a careful determination of the lowest temperature 

 recorded. Finally weigh the inner beaker and its 

 contents. 



In an actual determination, the following observa- 

 tions were made : 



Weight of beaker 



84-6 g. 



and water . . . . 308' 9 g. 



after adding ice 335*6 g. 



