Sir William Ramsay, the discoverer of terrestrial helium |
The
first evidence of helium was observed on August 18, 1868, as a bright yellow
line with a wavelength of 587.49 nanometers in the spectrum of
the chromosphere of the Sun. The line was
detected by French astronomer Jules
Janssen during a total solar
eclipse in Guntur, India. This
line was initially assumed to be sodium. On October
20 of the same year, English astronomer Norman
Lockyer observed a yellow line in the solar spectrum, which he named
the D3 Fraunhofer line because it was near the known
D1 and D2 lines of sodium. He concluded
that it was caused by an element in the Sun unknown on Earth. Lockyer and
English chemist Edward Frankland named the element with the
Greek word for the Sun, (helios). In 1881, Italian physicist Luigi
Palmieri detected helium on Earth for the first time through its D3 spectral
line, when he analyzed a material that had been sublimated during a recent
eruption of Mount Vesuvius.
On
March 26, 1895, Scottish chemist Sir
William Ramsay isolated helium on Earth by treating the mineral cleveite (a
variety of uraninite with at least 10% rare earth elements) with mineral acids. Ramsay was
looking for argon but,
after separating nitrogen and oxygen from
the gas liberated by sulfuric acid, he noticed a bright yellow line that
matched the D3 line observed in the spectrum of the Sun. These
samples were identified as helium by Lockyer and British physicist William
Crookes. It was independently isolated from cleveite in the same
year by chemists Per Teodor Cleve and Abraham
Langlet in Uppsala, Sweden, who collected enough of the gas to
accurately determine its atomic
weight. Helium was also isolated by the American geochemist William Francis Hillebrand prior to
Ramsay's discovery when he noticed unusual spectral lines while testing a
sample of the mineral uraninite. Hillebrand, however, attributed the lines to
nitrogen. His letter of congratulations to Ramsay offers an interesting
case of discovery and near-discovery in science.
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