16 



THE GROWTH OF SCIENCE 



material, wood. When the particles become so small that they 

 can be seen only with an ultramicroscope, they are called mole- 

 cules. The physicist calls everything that occupies space, matter; 



and he thinks of matter as 

 being made up of tiny 

 molecules in motion. 



The chemist takes sub- 

 stances or matter still fur- 

 ther apart. Water, wood, 

 rocks, air, our world in gen- 

 eral, may be taken apart 

 and separated into ninety- 

 two or more different sub- 

 stances called elements. 

 Ninety of these have been 

 separated from their com- 

 pounds and studied. Most 

 of the materials of the 

 world, including living things, exist in the form of compounds, com- 

 binations of elements. The chemist has worked out methods for 

 decomposing the compounds in order to study their constituents. 

 If an electric current is passed through water, it will cause the 

 liquid to be separated into two gases. If these two gases are col- 

 lected in tubes we find that twice as much gas will collect in one 

 tube as in the other. Both gases are colorless, odorless, and taste- 

 less. If a glowing splint is thrust into the tube containing the 

 smaller amount of gas, it will burn brightly the gas supports com- 

 bustion. It is oxygen. If a lighted splint is held near the tube 

 holding the larger volume of gas, there is a slight explosion and 

 the gas burns with a blue flame. It is hydrogen. Water has been 

 separated into its elements, hydrogen and oxygen, and is shown 

 to consist of twice as much hydrogen as oxygen. The molecules 

 of these elements may further be divided into atoms. The chemist 



Biology is related to chemistry and physics. The 

 topics embraced by both biology and chemistry have 

 been organized as a special science, bio-chemistry. 

 Note the other combinations shown in the diagram. 



