44 INTRODUCTION TO GENERAL SCIENCE 



EXPERIMENT FOR THE HOME 



Temperature Causes Cooking 



a. Place an egg in boiling water and boil it for exactly four 

 minutes. Open the egg immediately after removing it from 

 the water and note its texture. 



6. Place another egg in one pint of boiling water and re- 

 move from the source of heat. Allow egg to remain in the 

 cooling water for ten minutes. Open egg immediately and 

 compare it with the first egg. How much water would be 

 necessary to cook eight eggs by this method ? Would there 

 be any difference in the result if the egg had been in an ice- 

 chest? 



Eggs cooked at a lower temperature are not only pleasanter 

 to eat than eggs boiled rapidly, but they are also more digesti- 

 ble; that is, the consumer obtains more nourishment from such 

 an egg at less expenditure of digestive energy. 



30. CHEMICAL AND PHYSICAL CHANGES 



Changes within the molecule which alter its composition 

 are called chemical changes. After such changes the material 

 is entirely different from what it had been, and is, in fact, a 

 new substance. Examples of chemical change are the souring 

 of milk, decay of food, rotting of wood, formation of coal from 

 wood, destructive distillation, the bleaching of any material, 

 and any action which involves a permanent change. 



Physical changes are concerned with the molecules as a 

 whole, and are limited to the different arrangement of the 

 molecules, or their relative velocities. Physical changes are 

 often temporary, such as the melting of ice and the freezing 



