Helium is relatively abundant in many minerals, all of which are radioactive, and contain uranium or thorium as important constituents.
Strutt has suggested that helium in hot springs may be derived from the disintegration of common rocks at great depths.
Helium is present in the atmosphere, of which it constitutes four parts in a million.
Certain stars and nebulae show a bright line helium spectrum.
Much the best practical source of helium is thorianite, a mineral imported from Ceylon for the manufacture of thoria.
It dissolves readily in strong nitric acid, and the helium contained is thus liberated.
In order to get rid of hydrogen, some oxygen is added to the helium, and the mixture exploded by an electric spark.
Helium alone refuses to be absorbed, and it can be pumped off from the charcoal in a state of absolute purity.
In the absence of liquid air the helium must be purified by the methods employed for argon (q.v.).
A part of the helium contained in minerals can be extracted by heat or by grinding.
Properties.--All attempts to make helium enter into stable chemical union have hitherto proved unsuccessful.
Jacquerod and Perrot have found that quartz-glass is freely permeable to helium below a red-heat (Comet.
The density of helium has been determined by Ramsay and Travers as 1.98.
The refractivity of helium is 0.1238 (air =1).
The spectrum of helium as observed in a discharge tube is distinguished by a moderate number of brilliant lines, distributed over the whole visual spectrum.
The following are the approximate wave-lengths of the most brilliant lines: When the discharge passes through helium at a pressure of several millimetres, the yellow line 5876 is prominent.
At atmospheric pressure the discharge is able to pass through a far greater distance in helium than in the common gases.
Thus at high temperatures a helium thermometer is of no special advantage.
At low temperatures, on the other hand, they find, using an initial pressure of 'coo mm., that the temperatures on the helium scale are measurably higher than on the hydrogen scale, owing to the more perfectly gaseous condition of helium.
The liquefaction of helium was achieved by H.
- A bibliography and summary of the earlier work on helium will be found in a paper by Ramsay, Ann.
About the beginning of the 10th century, however, the view was promulgated that the spontaneous production of helium from radium may be an instance of the transformation of one element into another.
In 1894 he was associated with Lord Rayleigh in the discovery of argon, announced at that year's meeting of the British Association in Oxford, and in the following year he found in certain rare minerals such as cleveite the gas helium which till that time had only been known on spectroscopic evidence as existing in the sun.
Turning to the study of radioactivity, he noticed its association with the minerals which yield helium, and in support of the hypothesis that that gas is a disintegration-product of radium he proved in 1903 that it is continuously formed by the latter substance in quantities sufficiently great to be directly recognizable in the spectroscope.
The elements are usually divided into two classes, the metallic and the non-metallic elements; the following are classed as non-metals, and the remainder as metals: Of these hydrogen, chlorine, fluorine, oxygen, nitrogen, argon, neon, krypton, xenon and helium are gases, bromine is a liquid, and the remainder are solids.
The first, made by Sir William Ramsay in 1896, was that the mineral evolved a peculiar gas when treated with sulphuric acid; this gas, helium (q.v.), proved to be identical with a constituent of the sun's atmosphere, detected as early as 1868 by Sir Norman Lockyer during a spectroscopic examination of the sun's chromosphere.
It is found that mercury vapour, helium, argon and its associates (neon, krypton, &c.) have the value 1.67; hence we conclude that these gases exist as monatomic molecules.
Algol gives a helium-spectrum which undergoes no alteration at minimum.
Paschen 6 has further extended the method and added a number of infra-red lines to the spectra of helium, argon, oxygen and other elements.
In the case of helium one line was found with a wave-length of 20,582 A.
The conclusion which was originally drawn from this fact that helium is a mixture of two gases has not been confirmed, as one of the spectra of oxygen is similarly constituted.
Dorn 5 has found the Doppler effect with a number of lines of helium, which contain representatives of the trunk series as well as of the two branch series.
It may be added that helium has the same character as argon in respect of specific heats (Ramsay, Proc. Roy.
21, referred to air, somewhat higher than for oxygen, which stands at the head of the list of the principal gases ("On some Physical Properties of Argon and Helium," Proc. Roy.
Travers have obtained evidence of the existence in the atmosphere of three new gases, besides helium, to which have been assigned the names of neon, krypton and xenon.
Radium itself emits three types of rays: (1) the a rays, which are regarded as positively charged helium atoms; these rays are stopped by a single sheet of paper; (2) the s rays, which are identified with the cathode rays, i.e.
With Regard To The Scale Of Temperature, There Is Very General Agreement That The Absolute Scale As Realized By The Hydrogen Or Helium Thermometer Should Be Adopted As The Ultimate Standard Of Reference.
This Appears To Be Actually The Case For Monatomic Gases Such As Mercury Vapour (Kundt And Warburg, 1876), Argon And Helium (Ramsay, 1896).
Into two divisions, called helium and hydrogen stars respectively.
The former are often called " Orion " stars, as all the brighter stars in that constellation with the exception of Betelgeux belong to the helium type.
Some authorities, however, consider the Antarian (Type III.) stars to be in a very early stage of development and to precede the helium stars in the order of evolution; in that case they are in the stage when the temperature is still rising.
The stars of the Helium type of spectrum are remarkable for the smallness of their velocities; from spectroscopic observations of over 60 stars of this class, J.
The group consisting of five stars of Ursa Major together with Sirius has already been alluded to; another very marked group of 16 stars in Perseus, all of the Helium type of spectrum, form a similar association.
McClean, of the stars brighter than magnitude 3.5, only the helium and not the hydrogen stars of Type I.
Thus we see that the effect of limiting the magnitude to 3.5 is that the hydrogen stars are now practically all within the sphere SP, and it is only the helium stars, whose absolute luminosity is still greater, that are more widely distributed.
In the higher chromosphere the following were recognized: helium and parhelium, hydrogen, strontium, calcium, iron, chromium, magnesium, scandium and titanium.
In the higher chromosphere on occasions metallic gases are carried up to such a level that without an eclipse a bright line spectrum of many elements may be seen, but it is always possible to see those of hydrogen and helium, and by opening the slit of the spectroscope so as to weaken still further the continuous spectrum from the photosphere (now a mere reflection) the actual forms of the gaseous structures called prominences round the sun's rim may be seen.
In the visual spectrum there are four hydrogen lines and one helium line in which the actual shapes may be examined.
The helium formations do not reach the sun's limb, and it is another puzzling detail that the spectrum of the disk shows no absorption line of anything like an intensity to correspond with the emission line of helium in the chromosphere.
It is virtually identical with a group known as the " yellow stars," of which the most prominent examples are Capella, Pollux and Arcturus; this is not the most numerous group, however; more than one half of all the stars whose spectra are known belong to a simpler type in which the metallic lines are faint or absent, excepting hydrogen and sometimes helium, which declare themselves with increased prominence.