th the oxygen to form copper oxide, which is a
solid. The nitrogen passes on and may be collected over water.

~Nitrogen obtained from air is not pure.~ Inasmuch as air, in
addition to oxygen and nitrogen, contains small amounts of
other gases, and since the phosphorus as well as the copper
removes only the oxygen, it is evident that the nitrogen
obtained by these methods is never quite pure. About 1% of the
product is composed of other gases, from which it is very
difficult to separate the nitrogen. The impure nitrogen so
obtained may, however, be used for a study of most of the
properties of nitrogen, since these are not materially affected
by the presence of the other gases.

~Preparation from compounds of nitrogen.~ Pure nitrogen may be obtained
from certain compounds of the element. Thus, if heat is applied to the
compound ammonium nitrite (NH_{4}NO_{2}), the change represented in the
following equation takes place:

NH_{4}NO_{2} = 2H_{2}O + 2N.

~Physical properties.~ Nitrogen is similar to oxygen and hydrogen in that
it is a colorless, odorless, and tasteless gas. One liter of nitrogen
weighs 1.2501 g. It is almost insoluble in water. It can be obtained in
the form of a colorless liquid having a boiling point of -195 deg. at
ordinary pressure. At -214 deg. it solidifies.

~Chemical properties.~ Nitrogen is characterized by its inertness. It is
neither combustible nor a supporter of combustion. At ordinary
temperatures it will not combine directly with any of the elements
except under rare conditions. At higher temperatures it combines with
magnesium, lithium, titanium, and a number of other elements. The
compounds formed are called _nitrides_, just as compounds of an element
with oxygen are called _oxides_. When it is mixed with oxygen and
subjected to the action of electric sparks, the two gases slowly combine
forming oxides of nitrogen. A mixture of nitrogen and hydrogen when
treated similarly forms ammonia, a gaseous compound of nitrogen and
hydrogen. Since we are constantly inhaling nitrogen, it is evident that
it is not poisonous. Nevertheless life would be impossible in an
atmosphere of pure nitrogen on account of the exclusion of the necessary
oxygen.

~Argon, helium, neon, krypton, xenon.~ These are all rare
elements occurring in the air in very small quantities. Argon,
discovered in 1894, was the first one obtained. Lord Rayleigh