’ 
ACTIVITIES COMMON TO ALL ANIMALS. 27 
tube containing oxygen thrust a glowing coal (carbon) 
and see that it relights. Water is composed of two 
gases. Hydrogen burns easily in air, and oxygen aids 
the burning of hydrogen, of carbon, and of other sub- 
stances. 
Elements and Compounds. Because hydrogen and 
oxygen cannot be further separated into other sub- 
stances they are called elements. Water, because it 
is formed by the union of two elements, is called a 
compound. Carbon is also an element. 
Experiment. The Oxidation of Magnesium. Mag- 
nesium is anelement. To a piece of wire made of this 
element apply a lighted match and notice the produc- 
tion of heat and light. Examine the white powder 
produced. The oxygen from the air has united with 
magnesium and formed magnesium oxide. This white 
powder, the magnesium oxide, weighs more than the 
magnesium used. The process is oxzdatzon. 
The oxidation of hydrogen produces hydrogen oxide, 
or water. The oxidation of carbon produces carbon 
oxide, commonly called carbon dioxide. Magnesium 
oxide is a solid, hydrogen oxide is a liquid, and carbon 
dioxide is a gas. In all cases heat and energy are 
produced by oxidation. 
Experiment. The Oxidation of Phosphorus. Phos- 
phorus is an element obtained from the bones of ani- 
mals. Caution must be used in experiments with 
phosphorus as it ignites so readily. Remove a piece 
of phosphorus from the water and allow it to dry ona 
piece of blotting-paper. Note the smoke arising. This 
is phosphorus oxide. Touch the phosphorus with a 
warm wire. Note the increased rapidity of the oxida- 
tion. The same amount of heat is produced by the 
oxidation of phosphorus whether the oxidation is slow 
or rapid. Phosphorus oxide is formed in both cases. 
Experiment. Nitrogen in the Air. Air is almost 
wholly a mixture of nitrogen and oxygen. Cover the 
top of a large cork with asbestos and put on it a small 
