GENERAL INTRODUCTION 



PRELIMINARY EXPERIMENTS 



These experiments are inserted for those pupils who have not 

 had instruction in chemistry and physics, to give them a point of 

 view on the subjects that follow. At least a general understanding 

 of some of these subjects is necessary to a satisfactory elementary 

 study of biology. 



Elements and Compounds. — The material world is made 

 up of elements and compounds. An element is a sub- 

 stance that cannot be separated into two or more sub- 

 stances. A compound is formed by the union of two or 

 more elements. All the material or substance of which 

 the earth and its inhabitants is composed is formed of the 

 chemical elements ; this substance taken all together is 

 known as matter. 



Carbon and iron are examples of elements. Compare a 

 bit of charcoal, which is one form of carbon, with a new 

 iron nail. Which is brighter ? Heavier for its size ? 

 Tougher ? More brittle ? Harder ? More readily com- 

 bustible ? Resistant to change when left exposed to air 

 and dampness ? There are two other forms of carbon : 

 graphite or black lead (used in pencils and stove polish); 

 and diamond, which occurs in crystals and is the hardest 

 known substance. Iron does not have varied forms like 

 carbon. Sulfur is another element. What is its color? 

 Has it odor? Taste? Will it dissolve in water? Is it 

 heavy or light ? Will it burn ? What is the color of 

 the flame ? Of the fumes ? Phosphorus, another element, 



