Wikipedia:Reference desk/Archives/Science/2023 December 24

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December 24

Which pure metal is more prone to corrosion in air: magnesium or samarium?

Title says it all really. I've seen conflicting reports, so it may depend on humidity and other conditions. Double sharp (talk) 04:54, 24 December 2023 (UTC)

Pure magnesium exposed to carbon dioxide in the air forms a surface layer of magnesium oxide that protects the metal from further corrosion by air. Under humid conditions pure samarium gets a surface layer of samarium(III) oxide, but, according to our article on this oxide, "this oxide layer spalls off the surface of the metal, exposing more metal to continue the reaction".  --Lambiam 10:09, 24 December 2023 (UTC)

Damn: that set of samarium teaspoons I bought was probably a bad idea. {The poster formerly known as 87.81.230.195} 90.205.111.170 (talk) 00:31, 25 December 2023 (UTC)

Interesting. If Sm isn't air-stable, then it provides a nice mnemonic for the 4f row: the first seven (La–Eu) rust away completely in air (though at varying speeds), while the second seven (Gd–Yb) don't because the oxide layer protects them. Double sharp (talk) 03:41, 25 December 2023 (UTC)

I was just saying to my brother that all I want for Christmas is a nice mnemonic for the 4f row. —Tamfang (talk) 20:54, 26 December 2023 (UTC)

From personal experience---by far it is Samarium. — THORNFIELD HALL ^(Talk) 09:48, 28 December 2023 (UTC)

Thanks for the firsthand report! Double sharp (talk) 12:34, 28 December 2023 (UTC)

Follow-up regarding the next questionable entry in the 4f row: our article on gadolinium says that the oxide layer spalls off, but the source does not actually contain this claim. So, is it really true? (Later metals in the series are said to be relatively stable in air and only tarnish.) Double sharp (talk) 12:46, 28 December 2023 (UTC)

Etymology of hydrogen

When was the word hydrogen (or hydrogène) coined and by whom? Our article on the element says it was 1783 by Antoine Lavoisier. A discussion on the talk page suggests that the earliest instance of the word was 1787 and that Louis-Bernard Guyton de Morveau might deserve credit as well. This paper supports that conclusion, drawing on another 1947 paper by Harold Hartley which says "The name of hydrogen was not adopted until the whole nomenclature was revised four years later." (in 1787). gobonobo ^{+ c} 16:24, 24 December 2023 (UTC)

The French Wikipedia has an article on the treatise Méthode de nomenclature chimique by Morveau and others, published in 1787. The etymology section for hydrogène of the TLFi only mentions the 1787 treatise.^[1] While this may have been the first publication using the term hydrogène,^[2] Lavoisier praises Morveau in the introduction of this treatise for his major role in designing the new nomenclature. Morveau himself uses the spelling Hidrogène.^[3] Since he explicitly credits Lavoisier for the name oxygène, it is unlikely the name hydrogène is due to specifically Lavoisier. Morveau acknowledges the role of unnamed members of the Académie, as does Lavoisier in the introduction. Morveau published a treatise on the nomenclature in 1782;^[4] it would be interesting to see which name he proposed there for "the base of inflammable air".  --Lambiam 19:32, 24 December 2023 (UTC)

Thank you Lambiam. This is very helpful. gobonobo ^{+ c} 16:13, 25 December 2023 (UTC)

Does calculating the (upper bound of) neutrino mass, rely (also) on the mass energy equivalence?

HOTmag (talk) 18:15, 24 December 2023 (UTC)

Not that I know of, what gave you hat idea? NadVolum (talk) 18:52, 24 December 2023 (UTC)

I know that it's not that simple to calculate the neutrino mass, for example it was only possible to calculate the sum of squares of the masses of all three types of neutrinos, and that what the physicists have only achieved is the upper/lower bounds of this sum. For some reason (which is a bit complicated to tell here about) I wanted to know if those calculated values were calculated directly (e.g. by rules related to inertial mass or to gravitational mass and likewise), or indirectly - i.e. by calculating the neutrino energy and then by using the mass energy euivalence.

What did you mean by saying "Not that I know of"? Have you ever dealt (in depth) with the neutrino issue? HOTmag (talk) 22:29, 24 December 2023 (UTC)

Neutrino masses cannot be calculated, they have to be measured, and the measurements are rather indirect. What is calculated is how some observable quantity depends on the neutrino mass; these predictions are then compared to observations or experimental results to derive a best-fit value for the masses (or upper or lower limit if the measurements are not sufficiently sensitive to distinguish between different mass values). There are two main methods as indicated in the artice you linked to. The first is the observation of neutrino oscillations, which involves the computation of quantum mechanical transition probabilities. I suspect that these computations are not impossible to understand for someone who's done a course or two in quantum mechanics, but I haven't looked at them in detail myself. The other method uses the temperature fluctuation spectrum of the cosmic microwave background. The full computations here are very complex and involve several parameters in addition to the neutrino mass, but according to [5] the constraints on the neutrino masses come essentially from the suppression of small-scale fluctuations compared to large-scale fluctuations. Up to you to decide whether any of this fits in with your directly/indirectly dichotomy. --Wrongfilter (talk) 23:59, 24 December 2023 (UTC)

Thank you for the new link. The first method you mentioned is used for calculating the lower limit, which I didn't ask about. Before I asked my question, I had already seen the second method indicated in the article I linked to, and I had also read the abstracts of the sources linked to in that article (while the full researches are not available in the web), but unfortunately those abstracts, as well as the new article you've added, don't hint if the way to measure the upper limit (I actually asked about) relies also on the mass energy equivalence. HOTmag (talk) 08:40, 25 December 2023 (UTC)

You'd do better to engage with people in a cooperative way rather than complaining. Your question might as well have been one of the productions of The Engine from Gulliver's Travels and the article didn't mention anything like that, and yet you just attack when asked how you came by it. Why should anyone bother answering? NadVolum (talk) 22:14, 25 December 2023 (UTC)

What? Complain? Attack? I'm quite surprised. My first words to the only user who gave me the new link, were "Thank you". I tried to find any words of any attack or of any complaint, but found nothing, so I'm a bit confused now about what you meant.

Maybe you've ascribed - a complaint or an attack - to me, becuase of the (actually) innocent question I asked you, which you didn't interpret well? So let me be clear: I asked this question - about whether you had dealt (in depth) with the neutrino issue, just out of curiosity and hope, after I had read your first response "not that I know of": Your first response made me hope (and I still hope) you were a person who had dealt (in depth) with the neutrino issue: I thought that if you were the person I was looking for, I would ask you (on your talk page) some further questions about the neutrino. That's why I asked you the question mentioned above (which you haven't answered yet BTW). Anyway, if you are not the person I'm looking for (even though I still hope you are), I will be grateful if you could tell me about such a person, because I have some other questions about the neutrino.

HOTmag (talk) 08:04, 26 December 2023 (UTC)

None of the methods used to derive limits on the neutrino masses uses the mass-energy equivalence explicitely and primarily. However, the cosmological methods do rely on special and general relativity, of which mass-energy equivalence is also part. It becomes most explicit in the fact that particle masses contribute to the energy budget, i.e. have to be taken into account when writing down the energy density, which along with pressure is the source of gravity. That's almost trivial and doesn't describe the actual method, which rather tries to determine when neutrinos (from the cosmic neutrino background) became non-relativistic, i.e. when their average kinetic energy dropped below their masses (my preferred formulation is $\langle p\rangle \ll mc$). For a current list of upper limits to the sum of the neutrino masses see here (with indication of methods and data sets as well as links to the original papers); for a summary review see here (Sect. 26.2.3 and 26.2.4 in particular). Note that these methods constrain the sum of the masses; neutrino oscillations constrain the differences of squared masses. I'm not aware of any method that would constrain the sum of squared masses (but my knowledge of the topic is far from complete). --Wrongfilter (talk) 09:30, 26 December 2023 (UTC)

Thanks a lot. I appreciate your full answer. HOTmag (talk) 10:43, 26 December 2023 (UTC)