Argon

On Monday I was knocking off Henry's Law about the concentration of dissolved gases in solvents - typically water as it's an Environmental Science course.  So I compiled a list of the constituents of air, sorted from most to least abundant.

78.1%	Nitrogen	20.9%	Oxygen	0.93%	Argon	0.5-4%	Water
360ppm	CO2	18ppm	Neon	5ppm	Helium	1.7ppm	Methane
1ppm	Krypton	0.5ppm	Hydrogen	0.1ppm	Xenon	nowhere	The Rest

ppm is parts per million. Argon at 9% is 9000ppm. 

William Ramsey pointing at Argon

And as with every time I think about these data, I was struck by how abundant Argon is.  And also how many of the minor constituents of what we breathe are "inert" or "nobel" gases.  And then today I was told that it was William Ramsey's birthday (2nd Oct 1852, Glasgow).  I didn't realise, on Monday, I was channeling one of the greatest chemists of the 19th century - "Knock once for Yes, Sir William, or twice for No" <klok> <klok>: okay so I'm not channeling Sir William.  Whether or not, William Ramsey discovered Argon, then Helium, Neon, Krypton and Xenon between 1894 and 1896 and he won the Nobel Prize for Chemistry in 1904 "in recognition of his services in the discovery of the inert gaseous elements in air".  That's a whole column of the periodic table discovered by dogged perseverance, logical reasoning and meticulous instrumentation.

He found Argon first because it is the most abundant of the inert gases.  And he looked for it because of a niggling anomaly between the measured mass of Nitrogen (the gas N₂) derived from the air and Nitrogen (again the gas N₂) derived from other organic/terrestrial sources. Ramsey first heard about this from a public lecture by another great 19th Century scientist John Strutt aka Lord Rayleigh.  They had a chat after the lecture, went back to their respective homes and pulled out the stops on some great competitive-collaborative science. Air-derived Nitrogen appeared to be heavier.  As N₂ the gas is quite stable/inert it was hard to differentiate it from Argon which is really inert, but Ramsey and Strutt succeeded in doing this within the year.  The latter got the 1904 Nobel Prize for Physics "for his investigations of the densities of the most important gases and for his discovery of argon in connection with these studies". That's a pretty good haul for Argon.  Much later, after the Nobel prize, Ramsey went on to discover (radioactive) Radon, the last and least stable of the nobel gases about which I blogged before.

I've always thought that nobel gases are so called because of Nobel the Swedish dynamite/prize guy, imagining that their discovery round about the time the prizes were instituted, caused them to be named thus. In the same way as Mickey Mouse's dog was named after the (dwarf) planet Pluto which had been discovered earlier in the 1930. But that's nonsense - apparently, we use that term as a direct translation from the German Edelgas, so named because they didn't mix with the common or garden elements.  Nobel metals are the equivalent solids, also very unreactive: including Gold, Osmium and Rhodium.  And there is very little evidence that there was a conscious connexion between the two Plutos.

Argon is really important in the world of paleontology because potassium-40 decays to argon-40 with a half life of 1.25 billion years, so you can work out how old rocks are by measuring the relative abundance of these two isotopes.  Everybode kno about carbon-dating, a very similar process, but the half-life of carbon-14 is well under 6,000 years, so is useless for aging material beyond about 60,000 years ago.  K-Ar dating is good for much longer time-periods.

In my dogged research (channeling Ramsey again <not>, but punning like an Englishman - dog/Pluto geddit) this morning, I've just discovered that argon is used as an asphyxiant in the poultry industry - flood the chicken hangar with argon (cheap, inert, dense, hugs the ground, fills building from bottom) and the chucks all die because they have been deprived of (lighter) oxygen.  This is meant to be more humane, but I've watched lab mice being 'humanely' killed by flooding their cages with CO₂ (also denser than air) and it was not a pretty sight: it called to mind the Woody Guthrie lyric " bouncin' up and down like pop-corn poppin' " and they took a long time to die.  There, I'm glad I've got that off my chest.  In my distant youth, I was briefly cross-eyed about a great grand-daughter of John "Nobel" Strutt who went on to marry a descendant of Fleeming Jenkin, another very interesting scientific contemporary of Ramsey and Strutt. There, I'm glad I've got that off my chest, and I am really glad I'm not 16 anymore.