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 following methods: * 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.