AR'GON (Gk. 6pp5r, neut. of apy6f arpos, inactive, inert, alluding to its incapacity for entering into chemical combination). A gase ous element discovered in 1895 by Lord Ray leigh and William Ramsay, although CavendiTh had already mentioned it as a constituent of at mospheric air a century ago. Argon is contained the atmosphere to the extent of nearly 1 per cent. It was obtained by its discoverers by passing air through a combustion tube packed with metallic copper, which absorbed the oxygen. after which the gas was passed through an iron tube packed with magnesium turnings and heated in a combustion furnace. The mag nesium absorbed the nitrogen, and the argon, in its gaseous form, was then collected in a holder.
It was also obtained by adding oxygen to air, subjecting the mixture to the action of an elec tric current in the presence of an alkali, and removing all oxygen by means of pyrogallic acid. The density of the argon made by means of mag nesium was 19.94; that of argon prepared by the second method was 20.6 (the density of hydrogen being taken as unit, or rather that of oxygen as 10). The elementary nature of argon has been demonstrated by a comparison of its specific heats at constant pressure and at constant vol ume, which allowed that a molecule of argon is made up by a single atom and hence is not compound. But if this is true, then the molecu
lar weight (i.e. twice the density) of argon is identical with its atomic weight, and hence the latter is concluded to be about 40. Sir William Crookes found in the spectrum of argon two characteristic lines near the red end that could not be mistaken for the lines of nitrogen or of any other element. Argon cannot be liquefied unless its temperature is reduced at least 121 degrees below zero C. At —l21° C. a pres sure of 5041 atmospheres (759 pounds per square inch) is sufficient to produce liquefaction. Un der ordinary atmospheric pressure, liquid argon boils at —157° C. At the temperature of —190° C. it freezes. No well-defined chemical com pound of argon with other substances is as yet known. Its discoverers received the first Hodgkins Medal and the grand prize of the Smith sonian Institution at Washington. Consult : Lord Rayleigh and W. Ramsay, Argon, a New ronstitue»t of the Atmosphere, Smithsonian Con tributions to Knowledge (Washington, 1396).