Wikipedia:Reference desk/Archives/Science/2018 May 29

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May 29

Chemistry: Glass joint compatibility

Are conical ground glass joints compatible if they are the same diameter but have different lengths, i.e. can 24/29 joint combined with a 24/40 one? --188.23.204.47 (talk) 18:36, 29 May 2018 (UTC)

Yes, a short male in a long female will work. The other way round may not work depending on what is downstream of the female taper. Cue oh so hilarious frat boy humor. Greglocock (talk) 21:02, 29 May 2018 (UTC)

Because the taper is the same (1:10) if it fits for enough length to give the sealing desired without colliding with another art of the apparatus, they will fit snugly. Doesn't matter which is longer or which end(s) stick out. DMacks (talk) 04:54, 4 June 2018 (UTC)

Gas layer seperation

Our natural Air contains only 1% Argon but with 1.784 g/L, compared to the other 2 main components Oxygen (21% with 1.429 g/L) and Nitrogen (78% with 1.2504 g/L), it seems much heavier. All 3 Gases have considerable different weight. Thus without motion, air in a tank or cave should slowly separate in 3 layers of pure Argon on the ground, pure Oxygen in the middle and pure Nitrogen at the top. Is that correct or not and if not why? Thank you in advance for the answers. --92.231.161.94 (talk) 20:20, 29 May 2018 (UTC)

...without motion... Abductive (reasoning) 20:24, 29 May 2018 (UTC)

Just assume that means "without agitation". Someguy1221 (talk) 21:24, 29 May 2018 (UTC)

Not even all liquids separate into layers. This is observed with oil and water, for instance, because the two are immiscible. Specifically, water molecules bind extremely strongly to other water molecules, to the exclusion of oil. Mix water and ethanol, however, and they do not separate into layers. In a gas, by definition, the intermolecular bonds are very weak (indeed, for an ideal gas they are assumed to be totally absent). As a result, there is generally no such exclusion of one gas by another gas, although you can get temporary differentiation during the initial mixing of two gases. But over a long time period, everything diffuses everywhere, pretty much. Someguy1221 (talk) 21:51, 29 May 2018 (UTC)

Assuming the gasses are not interacting, both gasses just follow a vertical density profile based on molecular mass and gravity. This leads to a scale height. Now suppose one gas has twice the molecular mass of the other, then it has half the scale height. For example, if one gas has a scale height of 8 km in the atmosphere of a planet, the other will have a scale height of 4 km. This means that when rising 4 km in that atmosphere, the concentration of the dense gas will drop 63% compared to the concentration of the lighter gas. So you need a large difference in molecular mass and a big cave before you can see clearly different layers.

In reality the gasses do interact a bit and we have not only diffusion, but also (assuming there's flow) turbulent mixing, which mixes the gasses even better. So well, in fact, that in any realistic atmosphere that's not extremely dilute the different gasses have constant ratios.

Liquids are different because the molecules interact strongly. A water molecule surrounded by oil molecules is at a higher energy state than one surrounded by other water molecules, because when surrounded by oil it cannot make hydrogen bonds. PiusImpavidus (talk) 08:37, 30 May 2018 (UTC)

Going to much stronger "gravity", you can build a gas centrifuge. DMacks (talk) 21:14, 3 June 2018 (UTC)

E-nicotine vs. Devil's Tobacco - which is less dangerous?

It occurred to me recently that e-cigarettes, for all their chemical simplicity, produce N-nitrosonornicotine and other carcinogens directly produced from nicotine. Whereas Lobelia inflata (Devil's Tobacco, Indian tobacco, pukeweed etc.) does not contain nicotine, but something else (lobeline). When I did a moment's research I found that some e-cigarettes actually deliver lobeline: [1] Lobelia is sometimes said to be toxic, and sometimes gainsaid: [2] Which brings me to the main question: would smokers switching to smoking Lobelia leaves to satisfy their nicotine habit, which has been an option for hundreds of years, have a better overall outcome than smokers who switch to e-nicotine delivery? Has the question been addressed directly? Wnt (talk) 21:12, 29 May 2018 (UTC)

• I can't see how smoking a whole plant, be it tobacco, lobelia, cannabis, jimsonweed or nutmeg, could ever be less carcinogenic than vaping plant extracts. Abductive (reasoning) 21:58, 29 May 2018 (UTC)

@Abductive: Well, the thing about N-nitrosonornicotine is that it is tobacco (and e-nicotine!) specific. At least where cannabis is concerned I've been seeing mostly mumble about whether it causes cancer. I don't know if you can make a blanket generalization about burning plants causing cancer or not. Wnt (talk) 22:35, 29 May 2018 (UTC)

Each plant contains a plethora of chemicals, but an extract from that plant contains only a few. So it will be safer to inhale the extract. Abductive (reasoning) 23:18, 29 May 2018 (UTC)

While that seems likely to be true in many cases, I don't see how you can be sure that it's true in any individual case. What if one of the "few" substances in the extract happens to also be the most carcinogenic substance in the plant? While my non-expert impressions, derived from what I've read, are that this is unlikely to be the case for nicotine relative to smoke, I don't see how you can rule it out a priori. --Trovatore (talk) 23:23, 29 May 2018 (UTC)

Well, because while there are (allegedly) 600 chemicals in a cigarette, there are (allegedly) 7000 chemicals in the smoke. Also, plants are remarkably similar chemically (having myriad metabolic pathways in common, pathways without which living is impossible), so the idea that some are cleaner-burning than others seems unlikely. Abductive (reasoning) 23:43, 29 May 2018 (UTC)

There is at the very least an unstated step between counting the number of chemicals, and inferring the level of carcinogenicity. --Trovatore (talk) 00:18, 30 May 2018 (UTC)

And yet I'm still right. Abductive (reasoning) 01:12, 30 May 2018 (UTC)

And there's only one chemical in arsenic, so that must be healthy! I can see the point that for the same dose of the target chemical, the extract is likely to be healthier than the original plant (unless, of course, the plant happens to contain chemicals which enhance beneficial effects of the extract or mitigate negative effects, or the extraction results in a higher relative concentration of a non-target chemical). MChesterMC (talk) 15:36, 30 May 2018 (UTC)

Abductive seems to have confused being correct with being relevant. There are a billion correct statements one can make. They aren't all relevant to the discussion at hand. --Jayron32 16:23, 30 May 2018 (UTC)