ir is
allowed to boil, the constituents which are the most difficult
to liquefy, and which therefore have the lowest boiling points,
vaporize first, followed by the others in the order of their
boiling points. It is possible in this way to make at least a
partial separation of the air into its constituents, and Ramsay
thus succeeded in obtaining from liquid air not only the known
constituents, including argon and helium, but also the new
elements, neon, krypton, and xenon. These elements, as well as
helium, all proved to be similar to argon in that they are
without chemical activity, apparently forming no compounds
whatever. The percentages present in the air are very small.
The names, neon, krypton, xenon, signify respectively, new,
hidden, stranger.

EXERCISES

1. How could you distinguish between oxygen, hydrogen, and nitrogen?

2. Calculate the relative weights of nitrogen and oxygen; of nitrogen
and hydrogen.

3. In the preparation of nitrogen from the air, how would hydrogen do as
a substance for the removal of the oxygen?

4. What weight of nitrogen can be obtained from 10 l. of air measured
under the conditions of temperature and pressure which prevail in your
laboratory?

5. How many grams of ammonium nitrite are necessary in the preparation
of 20 l. of nitrogen measured over water under the conditions of
temperature and pressure which prevail in your laboratory?

6. If 10 l. of air, measured under standard conditions, is passed over
100 g. of hot copper, how much will the copper gain in weight?

[Illustration: WILLIAM RAMSAY (Scotch) (1855-)

Has made many studies in the physical properties of substances;
discovered helium; together with Lord Rayleigh and others he discovered
argon, krypton, xenon, and neon; has contributed largely to the
knowledge of radio-active substances, showing that radium gradually
gives rise to helium; professor at University College, London]

CHAPTER VIII

THE ATMOSPHERE

~Atmosphere and air.~ The term _atmosphere_ is applied to the gaseous
envelope surrounding the earth. The term _air_ is generally applied to a
limited portion of this envelope, although the two words are often used
interchangeably. Many references have already been made to the
composition and properties of the atmosphere. These statements must now
be collected and discussed somewhat more in detail.

~Air formerly regarded as