3io Common Science 



solutions are only mixtures and are not chemical com- 

 pounds. 



Everything in the world is made of atoms. Every- 

 thing in the world is either an element or a compound 

 or a mixture. Most plant and animal matter is made 

 of very complicated compounds, or mixtures of com- 

 pounds. All pure metals are elements; but metals, 

 when they are melted, can be dissolved in each other 

 to form alloys, which really are mixtures. Most of the 

 so-called gold and silver and nickel articles are really 

 made of alloys; that is, the gold, silver, or nickel has 

 some other elements dissolved in it to make it harder, 

 or to impart some other quality. Bronze and brass are 

 always alloys; steel is generally an alloy made chiefly 

 of iron but with other elements such as tungsten, of 

 which electric lamp filaments are made, dissolved in it 

 to make it harder. An alloy is a special kind of solution 

 not quite like an ordinary solution. 



You remember that in the opening chapters we often 

 spoke of molecules, the tiny particles of matter that are 

 always moving rapidly back and forth. Well, if you 

 were to examine a molecule of water with the microscope 

 which we imagined could show us molecules, you would 

 find that the molecule of water was made of three still 

 smaller particles, called atoms. Two of these would be 

 atoms of hydrogen and would probably be especially 

 small ; the third would be larger and would be an oxygen 

 atom. 



In the same way if you looked at a molecule of salt 

 under this imaginary microscope, you would probably 

 find it made of two atoms, one of sodium (Na) and one 



