23 



Can you suggest how a bottle might be made from a 

 closed glass tube ? 



Cheap dishes are made by pressing soft, plastic glass 

 into a die. Plate glass is made by pouring molten glass 

 on a level table, rolling it smooth with a hot metal cylinder, 

 and polishing it after it has hardened. 



Iron can be treated in a similar manner ; hence the forg- 

 ing of iron into numerous shapes is possible. 



How does the melting point of glass and of iron differ 

 from the melting point of most substances ? 



EXPERIMENT 12. THE HEAT LATENT IN ICE ; OR, THE 

 ABSORPTION OF HEAT BY MELTING ICE 



Weigh a glass beaker and after filling it with warm 

 water, weigh it again. The difference between these two 

 weights gives the weight of the water. Carefully note the 

 temperature of the water, and then drop a lump of dry ice 

 in the beaker. Stir the water until all the ice is melted, 

 then read the thermometer in order to find how much 

 the temperature of the water has been lowered by the ice. 

 Weigh the beaker and its contents and find the number of 

 grams of ice which have been melted in the water. 



All the heat used in melting the ice has been obtained from 

 the warm water originally in the beaker. Since the weight 

 of the water is known, and also the change in its tempera- 

 ture, we can determine the number of calories of heat lost 

 by the water in cooling. The heat thus lost by the water 

 was absorbed by the ice ; hence we can find the number of 

 calories abscrbed by the ice in melting. Finally we can 

 determine the number of calories absorbed by I gm. of ice in 

 melting. This is called the Latent Heat of Fusion of ice. 



