THE RARE GASES OF THE ATMOSPHERE. 193
of liquid air was mixed with oxygen and sparked over
soda, and the excess of oxygen was removed by phosphorus.
The remaining gas yielded a new and characteristic spectrum
(Proc. Royal Soc. LXIII, 437).
Occurrence.* Argon forms about one per cent, of the
air by volume. It is found in small quantities in gases
from certain mineral springs, e.g. Bath, Cauterets, Wild-
bad, Voslau, the sulphur spring of Harrogate; in the gases
occluded in rock salt, and in some volcanic gases (Moissan,
Compt. rend, cxxxvm, 936; cxxxv, 1085). It has been
detected in some helium-bearing minerals, e.g. cleveite,
broggerite, uratiinite, and inalacon.
Helium, the existence of which was first observed in
the sun, occurs in very small proportion in the terrestrial
atmosphere. The chief sources of the gas have been certain
rare minerals, among which are uraninite (pitch-blende),
cleveite, monazite, fergusonite, samarskite, columbite, and
malacon. It has been found also in some mineral springs,
e.g. Bath, Cauterets, Adano, and Wildbad, and in natural
and "'wind " gases in amounts varying from traces to 2%,
The gases yielding the largest percentages are those of
southern Kansas and northern Oklahoma.
The other gases of this group are present in the air in
very minute quantities. Neon is said to constitute 0.002 5%
and krypton 0.00002% of the atmosphere. Traces of neon
have been detected in the helium from the springs of Bath,
Extraction. Argon, contaminated with a greater or less
percentage of the associated gases, may be extracted by the
* See also Ramsay, Chem. News ixxxvn, 159; Nasini, Chem. Zentr. (1904)
n, 77; Pesendorfer, Chem. Ztg. xxix, 359; Rutherford, Chem. Zentr. (1905)
i, 848; Kohlschiitler, Ber. Dtsch. chem. Ges. xxxvin, 1419; Prytz, Chem. Zentr.
(1905) n, 1570; Ewers, Chem. Zentr. (1906) I, 1319; Moureu, Compt. rend,
CXLII, 1155; CXLIII, 795; Kitchin, Jour. Chem. Soc. LXXXIX, 1568; Czako, Ztschr.
anorg. Chem. LXXXII, 249; Chem. News cvm, 16; Collie, Jour. Chem. Soc. cin,
419; Piutti, Atti R. Accad. del Lincei, Roma  xxn, I, 140; Sieveking, Chem.
* Zentr. (1913) I, 58.