Letters: September 2018

Helium’s forgotten discoverer

The article on the history of helium was splendid (Chemistry World, August 2018, p50). I am a retired physical chemist whose research specialty was NMR spectroscopy, so over the years have greatly valued helium as an essential superconducting magnet coolant.

There are certain aspects regarding the discovery of helium on Earth that tend to be overlooked. The person who first identified terrestrial helium was not William Ramsay but Luigi Palmieri, an Italian physicist at the University of Naples, who identified the D₃ spectral line in gas associated with lava on Mount Vesuvius. Palmieri was an expert in seismological measurements of volcanoes and reported his finding in the rather obscure publication of the Royal Academy of Naples.¹ It seems unlikely that the astronomer Norman Lockyer was aware of this observation.

When William Ramsay isolated helium from a terrestrial source, the radioactive uraninite, he found it to be a totally inert gas. He was therefore prompted to write to Lockyer to suggest that, as it was a gas rather than a solid, it was more appropriate to name it ‘helion’, in accord with the other noble gases. Lockyer, not being a chemist, failed to appreciate the importance of systematic naming of chemical compounds, and the name ‘helium’ remained. When Ramsay first isolated this element in 1895 there is no evidence that he was aware of Palmieri’s earlier detection of terrestrial helium, but he certainly did become aware of it some years later – in 1909 he wrote an introduction to Recent Advances in Physical and Inorganic Chemistry, 1909, which reported Palmieri’s discovery.

Keith Orrell CChem FRSC
Sidmouth, UK

Reference

1 Palmieri L, R. Accad. Napoli, 1882, 20, 233

What a waste

I often read pieces in Chemistry World about the scourge of plastics (particularly single use plastics) on the environment. I can’t help but notice that your magazine, which must get sent to thousands of households every month, comes wrapped in plastic that can’t be recycled and so goes straight to landfill. It would be really wonderful if a switch to paper envelopes was made. Clearly, this would take some work to implement, but it would be a great move towards the sustainable distribution of Chemistry World and would make each issue a more enjoyable read.

Isabel Wilkinson
Oxford, UK

Editor: We’re considering a move to more eco-friendly materials, including oxo-degradable or starch bags. In the meantime, rest assured that the polywrap currently used is recyclable – just put it in the carrier bag recycle point at your local supermarket.

Mars and methane

It is wrong to state the 1976 Viking landers found no trace of organic compounds on Mars (Chemistry World, July 2018, p32). The GC–MS instruments aboard the landers detected chloromethane (CH₃Cl) and dichloromethane (CH₂Cl₂) at low levels of around 0.04–40 parts per billion (ppb).

While the Viking team concluded that the detected chloromethanes probably arose from pre-flight cleaning solvent contaminants, they did not rule out the possibility that they were indigenous to the examined Mars soil samples.

It is also unfair to say the detection of chlorinated organics by the Sample Analysis at Mars (SAM) suite aboard the current Curiosity rover wasn’t conclusive evidence of indigenous Martian organics. In spite of background contamination from leaking derivatisation reagents, the SAM team confirmed the presence of indigenous Martian organics in sedimentary rocks at Gale Crater, including the presence of chlorobenzene and chloroalkanes, at levels up to 300ppb by weight higher than can be explained by background contamination.

These chlorinated organics were interpreted as originating from indigenous Martian organics that were modified by reactions with chlorine gas, which results from the thermolytic breakdown of perchlorate salts at temperatures >250°C. These discoveries strongly indicate that the chlorinated methanes detected by the Viking landers were produced by the same processes. The presence of perchlorates and other oxychlorine compounds in Mars soils were first revealed by the wet chemistry laboratory on the Phoenix lander in 2008, and were unknown to the Viking scientists.

While the latest SAM findings of organic compounds are indeed fascinating, isolation of organic bio-signatures (if present) such as amino acids, fatty acids, carbohydrates and nucleobases will require a more refined analytical technique, such as capillary electrophoresis, and subtle solvent extraction prior to GC–MS analysis.

Kevin Devine MRSC
London, UK