Occurrence of Argon
|Argon is widely distributed in the free state in nature. As has already been mentioned, it is a constant constituent of the atmosphere. It forms 0.941 per cent, by volume of air freed from carbon dioxide and moisture, and 1.1845 per cent, by volume of atmospheric "nitrogen." The substantial accuracy of these figures has been verified by calculating the density of atmospheric nitrogen from them in conjunction with the known densities of pure argon and nitrogen. Results are thus obtained which agree closely with the values found experimentally by Rayleigh. |
The proportion of argon in the air appears to be constant, as samples taken from places as widely separated as Berlin, London, and Paris, and at heights varying from 0.5800 metres, contained amounts of argon varying between 0.932 and 0.935 per cent, by volume. Over the open sea, however, slightly higher proportions (up to 0.949 per cent.) have been found.
From the air argon finds its way into sea and river water, and because its solubility in water is greater than that of nitrogen, its proportion in the total dissolved gas is greater than in air. This greater solubility of argon will also explain why the proportion of argon in the gases from the air-bladders of fishes is always higher than in air and increases with the depth from which the fish is taken, and will account for the low proportion of argon in air taken from the soil. It has been found free in plants, and occurs in the blood of animals, but not in combination.
Argon has been found in the gas from the fumaroles of Mount Pelee (Martinique) and of Guadeloupe. It also occurs in the gases of many mineral springs, among which may be enumerated Wildbad, Black Forest; Perchtoldsdorf, Vienna; Reyjavik, Iceland; Allhusen's Well; Bath and Buxton; Old Sulphur Well, Harrogate; Strathpeffer Wells; Des (Eufs, Caesar and Espagnol Springs at Cauterets; Voslau; Monte Irone, Abano; Larderello, Tuscany; Poretta Baths, Bolognian Appenines; Mount Dore; Pevre, Ogen; Nehe and Trou des Pauvres, Dax; Vielle, Faux Bonnes; Saint Augustin, Panticosa; Maizieres, Cote d'Or; Raillere, Pyrenees; Bagnoles de l'Orne (4.5 per cent.).
Argon has been found in the natural gas of Kentucky, and in many specimens of fire-damp, in amounts which vary from 0.6 to 0.04 per cent, of the whole volume, but in almost every case are about 2 per cent, by volume of the nitrogen present.
If we now review the modes of occurrence of argon which have been enumerated, it will be found that in every case the gas occurs associated with nitrogen in proportions which are approximately of the same relative magnitude as the proportions of argon and nitrogen in the atmosphere. For example, brine from the rock-salt beds near Middlesbrough effervesces when it reaches the surface and gives off a gas which contains 98 per cent, of "nitrogen." This "nitrogen" contains about 1.24 per cent, of argon, i.e. about the same proportion as is contained in atmospheric nitrogen. It seems, therefore, probable that in all such cases the argon has been derived indirectly from the atmosphere.
It appears to be generally assumed that the atmospheric argon has existed in the elementary state since the earliest stages of the world's history.
But few minerals have been found hitherto which yield argon on heating: of these the chief are malacone, and another mineral from Brazil. It is noteworthy that both minerals contain large amounts of zirconium (malacone has the formula 3(ZrO2.SiO2).H2O, and the Brazilian mineral contains 97 per cent. ZrO2), and both are radioactive. Further, it is held by Antropoff that the amount of argon in the second mineral is too great to be derived from atmospheric sources. There is, therefore, at least a basis for the speculation that argon, like helium, may be a product of the disintegration of radioactive elements, but it must be borne in mind that the amount of argon present is quite small.
Argon has also been found in eliastite, and in a cerium mineral from Gov. Batum (South Caucasus).