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Members of the Argon Group

FROM a paper by Henry P. Talbot, published in the Technology Quarterly, M. I. Wilbert presents in the American Journal of Pharmacy the following facts and figures concerning the argon group: Argon.—The circumstances that led up to the discovery of this element may be found in the fact that Lord Rayleigh, in the course of some experiments, had noted that atmospheric nitrogen appeared to have a greater density than nitrogen obtained from chemicals, such as nitric acid, nitrous oxide or ammonium nitrite. Suggestions and explanations were numerous.--but unsatisfactory, and it was finally decided to determine whether or not there was an unknown heavier element in the atmospheric nitrogen. In making these inve!!:t.igations Lord Rayleigh had associated With” fiim Prof. Ramsay, of University College, London. After a long series of carefully planned and executed experiments, Lord Rayleigh and Prof. Ramsay, on January 31, 1895, made the announcement, at a meeting of the Royal Society in London, that they had discovered a new element in the atmosphere, to which, on account of its inert character, they had given the name argon. The quantity of this element, present in the atmosphere, appeared to be about 1 per cent of the contained nitrogen, or about 0.9 per cent of the atmosphere. Assuming that the density of argon was about 20, it would explain the greater density of atmospheric compared with chemical nitrogen. Argon has since then been found in one specimen of meteoric iron, in a variety of minerals and in the waters, or escaping gases, from a number of springs in different parts of Europe. So far it. has not been definitely demonstrated to have any chemical properties. Its physical properties, that is, its spectrum, its specific gravity, and the atomi-. city of its molecule have been the subject of much research and discussion. Its spectrum for instance appears to vary with the nature of the electrical energy that is used to energize the gas, and is admittedly complex and varied. This complex nature of the spectrum, as well as the accompanying variations, has been made a basis for arguments against the elementary character of argon. The density of argon has been carefully determined by Ramsay, who, as the result of numerous experiments, announced 19.96 as the true value for the density of the gas; this would correspond to a molecular veight of 39.92 (0 = 16). Helium.—This e'ement was first noticed in the spectrum of the chromosphere during an eclipse in 1868, by Janssen, who noted a brilliant yellow line, which was close to but not identical with the well-known D-line of sodium. This he designated as the Da-line, and in the same year Lockyer assigned the name “helium” to the hypothetical element, of which this line was characteristic. While this line has been repeatedly observed since then, by projecting the image of the edge of the sun on the slit of a spectroscope of wide dispersion, and has also been found in the spectrum of some of the fixed stars and nebulas, it had never been demonstrated to exist among terrestrial elements. After the discovery of argon, Mr. Myers, the mineralogist of the British Museum, wrote to Prof. Ramsay, calling attention to the fact that cleveite (a uranate of lead, thorium and uranium) had been shown by Hildebrand to contain nitrogen. Myers offered the suggestion that this mineral might contain argon or might have some constituent capable of entering into reaction with argon. This suggestion was later adopted by Prof. Ramsay, who demonstrated that the resulting gas, after removing the nitrogen, not only contained argon, when subjected to spectrum analysis, but showed a new series of lines in the red, green, blue, and violet and notably a brilliant yellow line. Ramsay later sent the gas to Crookes for examination and he in turn reported that the bright yellow lines were undoubtedly due to helium. Experiments made gave 3.89 as the maximum density of the gas, and the ratio of the specific heats was found to approximate 1.66. The gas is then, as was to be expected from its existence in the chromosphere, very light, and it appears to be monatomic. Helium has been found in a number of minerals almost all of which contain either uranium, yttrium oi thorium. It has been found in the gas emanating from several of the European thermal springs and has been definitely proven to exist in liquid air. From observations that have been made it has been determined that this element is one of the constituents of our atmosphere in the ratio of 1 or 2 parts in a million. The latest determinations of its density appear to make it about 1.98 and its atomic weight about 3.96. Other Members of the Group.—Prof. Ramsav. in a lecture before the Deutsche Chemische Gesellschaft In December, 1898, gave an account of the steps which led to the discovery of the other members of the group. The search for these elements was occasioned by an attempt to fit argon and helium into the periodic system. If 4 and 40 were assumed to represent the atomic weights of helium and argon respectively, there would be a space to be filled oy an element having an atomic weight about 16 higher than helium. The quest, begun by Ramsay and Collie and continued by Ramsay and Travers, opened with a careful re-examination of the minerals which had proved to be a source of helium. The search was later extended to other minerals of different chemical character, but with uniformly negative results. Meteorites and the gases from mineral springs were equally unproductive. Attention was then turned to argon, and its study in connection with liquid air. It was pointed out that the atomic weight of argon would be more tractable if it could be reduced to below 40, and a search after a constituent of the air having a lesser density than 20 seemed worth the making. In preparing to liquefy a quantity of purified argon, with the aid of liquid air, it was thought worth the while to examine the last fractions of some evaporating liquid air.' After removing the oxygen and the residual nitrogen, Ramsay found that there were present, in the spectrum of the residuJl.Y'gas, a number of the new lines, notably a yellow Une not identical with that of helium, and a new green line. The gas had a density of 22.5 instead of 20 and the ratio of specific heats of the mixture of gases was found to closely approximate 1.66. Here, then, was a new element or elements, but not the one sought for. Ramsay, assuming the presence of one only, gave it the name “krypton” (the concealed one). The gas has been studied more closely since that time. It is estimated to be present in the atmosphere in the ratio of about one part of gas to a million of air. The density of the gas is estimated to be about 40.78 and its atomic weight 81.56. .In the subsequent experiments that were made with liquid argon it was found that the first fraction, from the boiling argon, had a density of 14.67 and a ratio of specific heats of 1.66; the spectrum showed, besides the lines of argon, a number of new lines of red, orange and yellow of marked brilliancy. After some further separation of the contained argon the density was found to be 9.76. This new gas, which was designated as “neon,” while it still contained a fraction of argon, also contained helium, which would tend to decrease the density of the mixture somewhat. Later experiments appear to indicate that this gas has a density of about 9.96 and an atomic weight of about 19.92. It is present in the atmosphere to the extent of from 10 to 20 parts in a million. The less volatile portions of the liquefied argon they considered to contain at least two additional elements besides krypton and argon. To one of these they gave the name “xenon” (stranger), and while they did not have an opportunity to study it in a perfectly puro condition, they determined its density as being from 40.5 to 41.1. Later investigations appear to indicate that xenon has a density of about 64 and an atomic weight of 128. It must be considered as an extremely rare element occurring in the atmosphere in the proportion of 1-20 of 1 part to a million of air. The fourth component of the less volatile portion was given the name “metargon.” It was a source of much perplexity, as its spectrum was found to resemble the so-called “swan spectrum” of carbon monoxide. Subsequent study showed that the supposed new element was indeed carbon monoxide which had been introduced by accidental impurities in the chemicals. All of these elements are gases and all are chemically inert; it would appear self-evident, therefore, that they would form a distinct class of their own; but how to fit them into the existing periodic system developed a problem that has been attacked by several eminent European scientists, and has also been the cause of considerable discussion pro and con as to the elementary character of the substances, and the correctness of the available data concerning them. Several schemes have been proposed to fit them into the periodic system in a rational and satisfactory way. The one proposed by Ramsay is given below: H He Li Be 1 4 7 9 F Ne Na Mg 19 20 23 24 Cl A K Ca 35.5 40 39 40 Br Kr Rb 81' 80 82 85 87 I X Cs Ba 127 128 133 137 It will be noted that hydrogen, according to this arrangement, becomes the first element in the halogen group—a position for it which had been suggested by several eminent scientists. The inert group, according to this classification, would hold the position between the very active halogen and the sodium groups.—Druggists' Circular and Chemical Gazette.

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