,
an English scientist, while engaged in determining the exact
weights of various gases, observed that the nitrogen obtained
from the air is slightly heavier than pure nitrogen obtained
from its compounds. After repeating his experiments many times,
always with the same results, Rayleigh finally concluded that
the nitrogen which he had obtained from the air was not pure,
but was mixed with a small amount of some unknown gas, the
density of which is greater than that of nitrogen. Acting on
this assumption, Rayleigh, together with the English chemist
Ramsay, attempted to separate the nitrogen from the unknown
gas. Knowing that nitrogen would combine with magnesium, they
passed the nitrogen obtained from the air and freed from all
known substances through tubes containing magnesium heated to
the necessary temperature. After repeating this operation, they
finally succeeded in obtaining from the atmospheric nitrogen a
small volume of gas which would not combine with magnesium and
hence could not be nitrogen. This proved to be a new element,
to which they gave the name _argon_. As predicted, this new
element was found to be heavier than nitrogen, its density as
compared with hydrogen as a standard being approximately 20,
that of nitrogen being only 14. About 1% of the atmospheric
nitrogen proved to be argon. The new element is characterized
by having no affinity for other elements. Even under the most
favorable conditions it has not been made to combine with any
other element. On this account it was given the name argon,
signifying lazy or idle. Like nitrogen, it is colorless,
odorless, and tasteless. It has been liquefied and solidified.
Its boiling point is -187 deg..

Helium was first found in the gases expelled from certain
minerals by heating. Through the agency of the spectroscope it
had been known to exist in the sun long before its presence on
the earth had been demonstrated,--a fact suggested by the name
helium, signifying the sun. Its existence in traces in the
atmosphere has also been proven. It was first liquefied by
Onnes in July, 1908. Its boiling point, namely -269 deg., is the
lowest temperature yet reached.

The remaining elements of this group--neon, krypton, and
xenon--have been obtained from liquid air. When liquid a