The Preparation and some of the Properties of Pure Argon. 188 



It is thus evident that either set of figures gives results as concor- 

 dant as could be wished ; and that the density of " atmospheric " 

 nitrogen is correctly given as the mean of the densities of the con- 

 stituents, taken in the proportion in which they occur. 



''The Preparation and some of the Properties of Pure Argon." 

 By WILLIAM PtAMSAY, F.RS., and MORRIS W. TRAVERS. Ke- 

 ceived December 12, Eeacl December 15, 1898. 



In the memoir on Argon, a new constituent of the atmosphere,* by 

 Lord Rayleigh and one of us, reasons are adduced on pages 235 and 

 236 in favour of the supposition that argon is an element, or a mixture 

 of elements ; and on page 236, the following words occur : " There is 

 evidence both for and against the hypothesis that argon is a mixture, 

 for, owing to Mr. Crookes's observations of the dual character of its 

 spectrum ; against, because of Professor Olszewski's statement that it 

 has a definite melting point, a definite boiling point, and a definite 

 critical temperature and pressure ; and because on compressing the gas 

 in presence of its liquid, pressure remains sensibly constant until all 

 gas has condensed to liquid. The latter experiments are the well 

 known criteria of a pure substance ; the former is not known with 

 certainty to be characteristic of a mixture." And on pages 257-259 

 of the same volume, it is shown by Professor Sydney Young and one 

 of us, that the ratios between the boiling points of argon and benzene, 

 argon and alcohol, and argon and oxygen on the absolute scale are 

 such that it is possible _to compute the boiling points of argon at 

 different pressures with very considerable accuracy. We therefore draw 

 the conclusion : " It is hardly likely, though not impossible, that so 

 good an agreement would be obtained with a mixture or an impure 

 substance. It is, at any rate, certain that a distinct want of agreement 

 would have shown that argon was not a definite, pure substance, and 

 the results may be taken as affording additional confirmation of the 

 conclusion that argon is a definite, hitherto unknown constituent of the 

 .atmosphere, and that it has been isolated in a state very closely ap- 

 proaching to purity." 



The density of a sample of argon prepared by means of magnesium 

 was found by one of us to be 19'941 (0 = 16) ; and a much larger 

 preparation by Lord Rayleigh, obtained by exposing a mixture of air 

 and oxygen to an electric flame in presence of caustic soda, possessed 

 the density 19*94. Supposing argon to be a simple substance, and not 

 a mixture, the atomic weight would therefore be 39'88. An attempt 

 was made by Dr. J. Norman Collie and one of us to effect a separation 



* 'Phil. Trans.,' A, (1895), p. 187. 



