Discovery of Argon.
It might well have been thought impossible that any of the constant elements of atmospheric air, which has so frequently been analysed and examined by chemists and physicists in the foremost rank of science, could long have escaped detection, but, singularly enough, it was not until last year that the nitrogen of which it is so largely composed, amounting, in effect, to nearly four-fiths of its volume, was conclusively proved to be associated with an unknown chemical element. The compound character of atmospheric nitrogen had, however, long been suggested, and even to some extent demonstrated, by the older chemists, for we find that Berzelius, a contemporary
of Davy, satisfied that it was a compound body, was under, the impression that it was associated with an inflammable, base combined with oxygen, for which he proposed the name Nitricon. But he is said to have distrusted or abandoned this hypothesis in consequence of experiments made by Davy, who also believed that atmospheric nitrogen was a compound body, of which oxygen formed an element, and endeavoured, but in vain, to detach the latter by means of the vapour of potassium. But his experiments led only to the negative result that the divellent power of potassium was insufficient to overcome the affinity by which oxygen was held in combination with the other elementary matter associated with simple nitrogen. Mr. David Low, of Edinburgh, who published an important treatise on the “Simple Bodies of Chemistry,” in 1856, also treated atmospheric nitrogen as a compound substance, and mentioned that, from its known characters, the same opinion had long been entertained, but that, as all attempts to decompose it had failed, chemists had been content to acquiesce in regard to it, in their own maxim, that it must be regarded as simple because they had not been able to prove it compound, whilst he points out that all the known circumstances ought to have led to the juster conclusion that it should be treated as compound, although chemists had not been able to prove it so by means of the agents which they had employed to dissociate its elements. He also mentioned that, although it had theretofore resisted all attempts to dissociate it directly from the substance with which it was evidently compounded, there were reasons for believing that in many unheeded experiments in the laboratory its compound nature had manifested itself, especially in cases in which it was impossible otherwise to account for its presence.
But this point has now been set at rest by recent investigations made by Lord Rayleigh and Professor Ramsay, which have not only resulted in conclusively establishing the compound nature of atmospheric nitrogen, but also in showing that the substance with which it is associated is a gas previously unknown, to which they have given the name of argon. But the question, What is argon? still remains to be solved. So far as present researches into its chemical character have been carried, it is found to possess properties of so peculiar a description as to raise questions of paramount importance for chemistry.
It is well known that, prior to this discovery, Lord Rayleigh had been for many years engaged in inquiries as to the densities of several of the gases, and that he had found discrepancies in many of the results obtained which could only be accounted for in one of two ways,—namely, either by the occurrence of unavoidable errors in experiment or by the
assumption that some of the supposed simple bodies were in reality compound. These discrepancies were especially obvious in the ease of atmospheric nitrogen, for when obtained from that source by any of the methods usually employed for the purpose, it was invariably found to be heavier in an appreciable degree than when obtained from any other compound of which it formed a part. This would doubtless have been noticed by Berzelius, or Davy, or Faraday, who had also experimented on atmospheric nitrogen, had any of them compared its relative densities when obtained from that and other sources, such, for example, as ammonia, and yet the fact that nitrogen entered into the composition of ammonia was one of those which led some of the older chemists to infer its compound character. It would certainly be strange if Lord Rayleigh was unacquainted with these older speculations, although, so far as my reading goes, I have seen no reference to them in the published accounts of his experiments. The difference actually found by him between the weight of atmospheric nitrogen and that chemically obtained from its compounds was that its average weight in the former was 1.2572 grammes, whilst in the latter it was only 1.2505, a difference of ·0067 grammes. Many suggestions were offered to explain this discrepancy, all of which, however, were based upon the supposition that atmospheric nitrogen was the purer of the two, and that the nitrogen chemically prepared must still contain some lighter gas. But upon proper test experiments being applied in connection with these suggestions they were found to be untenable, and it soon became clear that the supposed position must be reversed, and that atmospheric nitrogen must have in combination some heavier gas previously unknown. For some time after this discovery the test of separating argon from the atmospheric compound proved to be a very difficult one. Nitrogen, chemically speaking, is an inert substance, by which is understood that it is very difficult to force it into combination with other substances, and it soon became obvious that argon could only be obtained as a residue after removing from any given quantity of atmospheric air all its other constituents. This was effected in several ways, all of which were slow and wearisome. It has, however, been justly remarked that “chemical bodies must be taken as we find them, and that those amongst them which, even in the hands of the best experimentalists, yield only to methods outside of ordinary chemical routine are precisely those whose investigation leads most to the extension of chemical knowledge.”
The chemical nature and properties of the new substance have as yet been only partially ascertained, the chief obstacle
to investigations into this branch of inquiry arising from the difficulty of obtaining it in sufficient quantity for experiment; and, in fact, what is known is chiefly negative. Mr. Crookes submitted it to spectrum analysis, the result of which led him to suppose that it consisted of a mixture of two gases; whilst the experiments of Olszewski into its temperature of liquefaction and its critical temperature and pressure seemed also to indicate that it is a compound substance, but that the mixture could only contain a very small proportion of another gas.
Its leading physical properties were more easily ascertained. It was found to be colourless and inodorous, to have a density of about twenty times that of hydrogen, although it is probable that this may be exceeded. It is more soluble in water than oxygen or hydrogen, and therefore it is not improbable that in drinking unboiled water we imbibe a proportionately larger quantity than we inhale in breathing. It requires a very low temperature for liquefaction, Professor Dewar having ascertained that it liquefies at 305° Fahr. below zero, and is converted into opaque ice at 310°. These physical properties, however, have as yet afforded little aid in determining its chemical nature; but, as this question is being investigated by some of the greatest chemists of the day, and, amongst others, by Mendeleeff, Berthelot, and Professors Dewar and Ramsay, we may expect to receive, within a reasonable time, full information in respect to it. In the meantime it is supposed to be a tri-atomic form of nitrogen, as ozone is a bi-atomic form of oxygen; and many circumstances already known—for example, its concurrent appearance in nature with nitrogen, the difficulty of separating them, their common inertness—exaggerated in argon—their common lines in the spectra, their double spectra, and the outer resemblance of their benzine compounds as shown in Berthelot's experiments —are said to lend strength to this hypothesis.
The announcement recently made by Professor Ramsay that he had discovered that argon is contained in a mineral called clevéite, is likely to lead to a rapid increase in our knowledge of its chemical character and properties. A bright-yellow line in the spectrum of the sun's chromosphere had long been observed with interest, and was generally ascribed to an element unknown on the earth, but widely spread on the sun, from which circumstance it had been called helium. Now, this element was lately captured by Crookes in a glass tube in the laboratory, quite unexpectedly, in the course of investigations which Professor Ramsay was making with a view to extracting and analysing the gas contained in clevéite, said to be nitrogen. He communicated his discovery to Professor Cleve, of Upsala (in whose honour the mineral had
been named by Nordenskjold), who at once extracted the New gas, which was submitted for spectroscopic examination to Thalen, one of the best spectroscopists of the day, who confirmed Crookes's statement, but found no trace of argon. Ultimately, however, Professor Ramsay, while boiling clevéite in weak sulphuric acid, not only obtained helium, but also argon, devoid of the gas which is usually found associated with atmospheric argon, and which may be the cause of the high density of the latter. Thus several new forms of gas have already been discovered, whilst more are apparently in view. From these facts it appears certain that the means now available for producing argon in a pure condition, coupled with the further discoveries made in the search for it, are sure to launch both chemistry and physics into a new domain of philosophical inquiry, which will not only materially widen our knowledge of facts and our theoretical views in chemistry, but will probably also lead to some more definite conceptions of the nature and structure of matter.