Argon having been discovered, chemists at once undertook to ascertain its chemical prop erties, but here they met with an obstacle that has not yet been overcome, and which consti tutes one of the strangest facts known to chem istry. It was found, namely, that argon can not be made to enter into chemical combination with any substance whatsoever. Thus Rayleigh and Ramsay have stated that °argon does not combine with oxygen in presence of alkali under the influence of the electric discharge, nor with hydrogen in presence of acid or alkali, nor when sparked, nor with phosphorus at a bright red heat, nor with sulphur. Tellurium may be distilled in it and also sodium and potassium. Red hot sodium peroxid has no effect. Persulphids of sodium and calcium have no effect at a red heat. Platinum sponge does not absorb it. Aqua regia, bromine water, bromine and alkali, and potassium permanga nate are all without influence. Mixtures of metallic sodium and silica, or of sodium and boric acid, are likewise without influence, and hence also nascent silicon and boron.° Mois san further found that fluorin does not act upon it at any temperature. In short, it may be said that every reagent that the previous ex perience of chemists indicated as likely to com bine with argon has been tried without success, and hence the chemical properties of the ele ment (if, indeed, it has any such properties), are as yet quite unknown. Several announce ments of the existence of compounds of argon have been made, but no really convincing evi dence of such combination has been given. For example, Berthollet subjected a mixture of argon and benzene to the action of the silent electric discharge for a long time, and observed a diminution in the volume of the argon, which he attributed to its combination with the benzene. Benzene when treated in this way forms a resinous mass, which coats the walls of the tube, and it is not improbable that the small quantity of argon which disappears is held mechanically by the gummy deposit, either in solution or by absorption. At all events the original quantity of argon is restored, un changed, by heating the resin. It cannot be positively affirmed that no compound of argon exists, but there is no previously known ele ment (not even the metals of the platinum group) that could withstand the action of the substances whose activity has been exerted without effect upon argon. Until some com pound can be formed we shall therefore have to infer the atomic weight of argon from de terminations of the density of the gas, taken in connection with Avogadro's law. The best
determinations made up to the present time in dicate that the density of argon is 19.942 times that of hydrogen. If the molecules of argon are diatomic, then 19.94 is the atomic weight of the element, but if they are monatomic, we must double this estimate and conclude that the atomic weight is 39.88 (see ATOMIC THEORY; also GASES, KINETIC THEORY OF). To settle this doubtful point experiments were made to find the ratio of the two specific heats of the gas, and it was found that the specific heat of argon at constant pressure is about 1.644 times as great as the specific heat at con stant volume. This indicates that the molecule of the gas contains but one atom, and hence it is necessary to conclude that the atomic weight of argon is the atomic weight of hydrogen being taken as 1. Argon has been liquefied and solidified. Its critical tempera ture is F. below zero, and its critical pressure is about 52.9 atmospheres. Liquid argon boils (under ordinary atmospheric pres sure) at about F. below zero, and at about below zero it freezes. The density of liquid argon is about 1.4046 at its boiling point. Four other elements, associated with argon in the air and closely resembling it in properties, have been discovered as the result of researches suggested by the discovery of argon. They are called, respectively, helium, neon, krypton and xenon (qq.v.). Hundreds of papers dealing with argon and the other gases just mentioned have appeared in the scientific periodicals, so that no bibliography of the subject can be at tempted here. Ramsay's book, The Gases of the Atmosphere' (1896) gives an excellent ac count of the chemistry of the air, from the earliest times down to 1896. It must be re membered, however, that our knowledge of i argon and its allies is growing rapidly, so that some of the statements that Ramsay makes can be no longer admitted to be true. For ex ample, he states that helium (which had al ready been discovered when his book was writ ten) does not occur in the air, but it has since been shown that it is a component of the air, forming from one to two one-millionths of its bulk. (See GASES, COMPRESSED). Travers' The Experimental Study of Gases) may also be consulted with advantage.