8 ELEMENTARY BIOLOGY 



making of soap, certain kinds of substance disappear and new 

 substances seem to arise. Changes of this character are called 

 chemical changes. 



10. Conservation of matter. Whether a change is chemical 

 or physical, the total aino7mt of substance remains the same. 

 A pound of ice melts to a pound of water and evaporates to 

 a pound of steam. A quantity of fat plus lye plus water will 

 produce the same total of soap plus glycerin plus water. The 

 total of the materials involved in a fire remains the same. 

 Modern science has been able to demonstrate this in many 

 cases. But whether it can be demonstrated in all cases or not, 

 this principle is assumed in all scientific reasoning about what 

 happens in the world ; indeed, it is the very foundation of 

 scientific thinking. 



The first law of matter is this : Matte}" can neither be 

 destroyed nor created. Or, stated differently, the quantity of 

 matter remains constant. 



11. Complexity of matter. If we examine a piece of granite 

 carefully, we see that it is clearly made up of several different 

 kinds of particles. In a piece of marble, however, all the par- 

 ticles seem to be of the same kind. Alcohol, or chloroform, 

 or water seems to be of the same kind of stuff all the way 

 through ; but it is easy to convince ourselves that milk, which 

 may appear to be one kind of stuff, is really made up of 

 several different kinds of matter. 



We see that we cannot always tell from the appearance of a 

 body whether it is made up of one kind of stuff or of several 

 kinds. Thus, if we took a piece of rock candy, a piece of clean 

 ice, a piece of clear glass, a crystal of quartz, and a diamond, 

 we should find that they all look very much alike. Yet these 

 five substances are quite different from each other in many 

 ways. The chemist is able to get from the glass certain sub- 

 stances ; some of these are present also in quartz, and one of 

 them is present in the ice (water) and in the rock candy 

 (sugar). From the water he can separate out two different 



