burning match placed in a corked bottle goes out as soon as it has
used up the oxygen in the bottle. The nitrogen in the bottle, not only
does not assist the burning of the match, but it acts as a damper to
the burning.

Free nitrogen, like oxygen, is a colorless, odorless gas. It is not
poisonous; but one would die if surrounded by nitrogen alone, just as
one would die if surrounded by water. The vast supply of nitrogen in
the atmosphere would be useless if the smaller amount of oxygen were
not present to keep the body alive. Nitrogen is so important a factor
in daily life that an entire chapter will be devoted to it later.

Another constituent of the air with which we are familiar is carbon
dioxide. In pure air, carbon dioxide is present in very small
proportion, being continually taken from the air by plants in the
manufacture of their food.

Various other substances are present in the air in very minute
proportions, but of all the substances in the air, oxygen, nitrogen,
and carbon dioxide are the most important.




CHAPTER VIII

GENERAL PROPERTIES OF GASES


85. Bicycle Tires. We know very well that we cannot put more than a