An Element of Interest...

Helium He 2 4.00260




Sir William Ramsay

The People's Almanac #2 by David Wallechinsky and Irving Wallace, William Morrow and Company, Inc., New York

Here is an interesting article written for Helium's 100th Aniversary.

Not many people know this, but 1995 is the 100th anniversary of the discovery of helium, the lighter-than-air gas that fills Mickey Mouse balloons and makes your voice sound like Donald Duck. Having a 100th birthday may not seem particularly remarkable--until you realize that helium is the second most common element in creation, accounting for one in every ten atoms in the Universe--which prompts the obvious question: how in the world did we manage to miss it until 1885?

The simple answer is that helium is both chemically inert and extremely light. Its inertness ensures that it rarely gets trapped in compounds, while its lightness means that as soon as it is released into the air it floats off into space.
And space is where the gas was first found. Helium is unique in being the only element to be discovered on the Sun before it was discovered on Earth. The man who spotted it there was Norman Lockyer, a civil servant from Wimbledon who, among other things, wrote the first book on the St. Andrew's rules of golf, founded London's Science Museum in South Kensington and launched the international science journal Nature, which he edited for 50 years.

On 20 October 1869, Lockyer pointed his 6-inch telescope at the sun and examined the light with a spectroscope. In the spectrum of a solar prominence he was surprised to see a curious yellow line. The line was observed the same year from India by the French astronomer Pierre Jules Cesar Janssen. Both men failed to reproduce the spectral feature in the laboratory and, in 1870, Lockyer make the bold suggestion that the line was the "fingerprint" of an unknown element. Lockyer was ridiculed for proposing the existence of "helium" and had to wait many years to see his critics silenced. The man who proved him right and found helium on earth was the Scottish chemist William Ramsay, the only person to discover an entire group of the periodic table of elements--the noble gases. It is the centenary of Ramsay's discovery, not Lockyer's that we are celebrating this year.

Norman Lockyer

In March 1895, while examining the spectrum of gases given off by a uranium mineral called cleveite, Ramsay spotted a mysterious yellow line. Lacking a good spectroscope, he sent gas samples to both Lockyer and to William Crookes, a physicist famous for experimenting on cathode rays and being an advocate of telepathy. Within a week Crookes had confirmed that the gas was the same as the one Lockyer had observed. Lockyer was beside himself with joy as he squinted through the spectroscope at the "glorious yellow effulgence" he had first seen on the Sun a quarter of a century before.

Today, helium is used in arc-welding equipment, lasers and gas-cooled nuclear reactors. Deep-sea divers avoid the bends by breathing a mixture of helium and oxygen. But helium's greatest claim to fame is as the ultimate refrigerant. Boiling at the lowest temperature of any substance--a mere 4.2 K or -269 oC--liquid helium is used to cool anything from astronomical detectors to superconducting magnets. In fact, in its liquid state, helium can lay claim to being one of the most bizarre substances known. when cooled below 2.18 K it becomes a superfluid, able to flow without friction, squeeze through impossibly small holes and even run up hills. Helium is also the only substance that never solidifies. Hell will freeze over long before liquid helium does.

But there is a final twist to the peculiar story of this peculiar substance. although most of the helium in the Universe was forged in the first few minutes of the big bang, with a small amount cooked later in stars, most of the helium on earth comes from the radioactive decay of heavy nuclei deep in the planet. some finds its way into deposits of natural gas.






This article was from NEW SCIENTIST written by Marcus Chown, author of THE MAGIC FURNACE (Oxford University Press, New York).

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