WHAT GOES ON IN THE WORLD 9 



substances, both of which are present also in sugar. But from 

 the diamond he can get only one kind of stuff, no matter what 

 he does with it ; and that stuff, called carbon, is present also 

 in sugar. 



12. Elements and compounds. The chemical changes that 

 take place when a substance is separated into simpler stuffs is 

 called analysis, which means a separation, or putting asunder. 

 The breaking up of water into oxygen and hydrogen, by means 

 of an electric current, is a kind of analysis. The chemical 

 change that takes place when two or more substances are com- 

 bined into a new substance is called a synthesis, which means 

 a placing together, or corn-posing. When hydrogen is burned 

 it combines with oxygen, and the two together form water. 



The substances which the chemists have not been able to 

 break up into simpler kinds of matter are called elements. A 

 combination of two or more elements is called a compound. 

 Many of the elements combine with one another very readily ; 

 as a consequence, most of the substances with which we are 

 familiar are compounds. A given set of elements may form a 

 large number of different compounds. Thus, hydrogen, oxygen, 

 and carbon can form an unlimited number of compounds, 

 depending not only upon the proportions in which they are 

 combined, but also upon the arrangement of the elements. 

 This we can readily understand when we think how a few 

 letters can make many different words, or how a given lot 

 of brick and mortar and wood can be combined into many 

 different kinds of structures. 



13. Energy. All the changes that we experience seem to 

 be brought about by the action of some kind of force. For 

 example, gravitation changes the positions of the earth and 

 the moon and so on ; heat changes the states of matter ; light 

 causes chemical changes in a photographic plate or in wall 

 paper. It is proper to speak of the force of gravity, of heat, 

 of light, of electricity, of magnetism. Each of these forces 

 is considered a form of energy, and any one of them can be 



