38 A YEAR IN SCIENCE 



The fact that ice in melting withdraws heat from the 

 surrounding objects is of value in many ways. The ice 

 in an ice chest, in melting, takes heat from the food 

 placed in the chest. When snow melts in the spring it 

 cools the air, and thus prevents the very rapid melting 

 of snow which might otherwise cause floods. 



Heat necessary to dissolve a substance. If a handful 

 of salt is placed in a glass full of water and very slowly 

 stirred with a thermometer, the temperature gradually 

 decreases as the salt dissolves. The salt is changing 

 from a solid to what may be considered a liquid. In 

 order to do this heat is necessary. In this experiment, 

 the heat comes from the water. 



In ice cream freezers the chopped ice is mixed with 

 coarse salt. Heat is taken from the cream not only to 

 melt the ice but also to dissolve the salt. As a result 

 the cream freezes. The mixture of salt and w r ater does 

 not freeze because its freezing point is below that of 

 pure water. 



Heat given off when liquids become solids. A flask 

 in which 50 grams of sodium hyposulphite and 10 c.c. of 

 water have been placed is heated slowly until all the 

 sodium hyposulphite is dissolved. The flask is then 

 removed from the flame, closed with a plug of cotton, and 

 very carefully set aside to cool. Care should be taken 

 that the flask and its contents are not disturbed for about 

 forty minutes. If the cotton plug is then removed, and a 

 thermometer is placed in the liquid, the solution at 

 once begins to crystallize. The hypo changes from 



