BUBaTANCEa WITHOUT CHEMISTRY 247
as a source of oxygen. liquid air consists mainly^ of course^ of nitrogen and oxygen and when it boils nitrogen volatilizes more readily than oxygen, just as alcohol distils off from water with which it is mixed. So oxygen is left behind just as water is left behind, a somewhat bluish liquid with the peculiar property of being magnetic. After the nitrogen, the oxygen volatilizes and when it has nearly gone the small quantity of liquid left is mainly argon but there is a little krypton and xenon. Bamsay and Travers used about six gallons of liquid air, Moore some time afterwards made use of the residue of a quantity of liquid air which will by most people be considered really large, namely, one hundred and twenty tons. There is one part of krypton in twenty million parts of air by Tolume and one part of xenon in one hundred and seventy million parts of air. Thus 120 tons of air would yield between twenty-five and thirty cubic inches of xenon and about eight times as large a volume of krypton. The latter name refers to the gas being hidden by or in the large quantity of argon which it closely resembles. There is a rare metal lanthanum whose name has a similar origin, since the properties of its compounds are so similar to those of another metal that it escaped notice for a considerable length of time.
The aurora horealis has been the object of admiration and speculation for centuries. Cavendish, whose connection with the main subject of this paper was so conspicuous, calculated the height of the aurora to be from fifty-two to seventy-one miles and probably this calculation is not far wrong. One of the theories regarding the cause of the aurora is that it 18 due to electrical discharge through the rarefied atmosphere and De la Bive of Geneva made a model to represent the discharge infiuenced by a magnet in much the same way as terrestrial magnetism affects the aurora.
When the aurora was examined by the spectroscope a very intense green line, not known to belong to any element, was found. When Bamsay was working with krypton, his assistant^ Baly, examined its spec- trum and noticed among a number of other liaes a brilliant green one whose WAve-length he measured carefully. No sooner were his results published than letters were sent to Bamsay and to the scientific press pointing out that this wave-length corresponded to that of the most im- portant Ime in the spectrum of the aurora.
Keon does not call for special comment It is lighter than air and has a spectrum not already known, perhaps receiving its name of new from this fact. There is one part in about 55,000 of air.
All these elements are incapable of forming compounds; they are all inert; they have no chemistry. The atomic weight of most elements is arrived at from chemical considerations, the analyses of compounds, and such like experiments. The atomic weight of these elements can not be arrived at in this way. The density as compared with hydrogen can be determined, but this alone will not fix the atomic weighty the relative
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