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September 16

Why there is no vent for medical oxygen tanks?

I remember seeing a vent on top of oxygen tanks at industries, but why there is no vent for medical oxygen tanks? Rizosome (talk) 03:49, 16 September 2021 (UTC)

Maybe the venting oxygen tanks you saw were for holding liquid oxygen, whereas medical oxygen tanks contain compressed gas. Here you can read about the need to vent liquid oxygen cylinders.  --Lambiam 07:05, 17 September 2021 (UTC)

A great link. Just to add that liquid oxygen would be far too cold to use in a medical setting, e.g. to assist breathing.--Shantavira|^{feed me} 08:28, 17 September 2021 (UTC)

For iron's metallic bond, what type of iron ion is present to bond with the delocalized electrons?

For sodium, each Na will lose 1 e- to form Na+. Then sodium ions are attracted to the delocalized electrons, and therefore there is metallic bond. However, for iron (and other transition metals), how many electrons will each iron atom lose? Will they lose all of the 4s electrons? Or, is the ion Fe(II) or Fe(III) ion? Thank you so much!!!! Jocosus2000 (talk) 15:04, 16 September 2021 (UTC)

• NaCl has ionic bonds. Those can be simplified as "one atom loses one (or more) electron(s) to another atom, and both stick together due to electromagnetic attraction". (For the longer explanation, see the linked article.)

Iron, on the other hand, has metallic bonding. A gross oversimplification is that iron atoms pool electrons together into a sea of free-moving electrons. Individual atoms do not really "lose" electrons in that process. How many free electrons per atom are yielded by that process is a good question, but not one I can answer - researching this probably goes through our article Valence and conduction bands; based on a sentence in Drude model I assume usually as many as the valence number (so, probably 3?).

Finally, many compounds have covalent bonding, where close-by atoms share some electrons, and shared electrons count for both atoms towards the "having a complete electronic shell" stability criterion. The difference with metallic bonding is that the electrons are not free-moving so the bond is really local. Tigraan^{Click here for my talk page ("private" contact)} 15:52, 16 September 2021 (UTC)

Thank you so much!!! By the way, is band similar to orbitals? Thanks:)Jocosus2000 (talk) 10:04, 17 September 2021 (UTC)

No. Atomic orbitals are a concept linked to a single atom (the "location" of a given electron, basically). The conduction/valence bands are macroscopic (or mesoscopic) concepts related to energy levels of a large number of electrons around a large number of atoms. Tigraan^{Click here for my talk page ("private" contact)} 12:06, 17 September 2021 (UTC)

Where an atom in a compound loses an electron to some other place in the structure, and it is just a single electron, that is called an electride. They're different to metals as they are insulators. Graeme Bartlett (talk) 12:41, 17 September 2021 (UTC)

Thank you so much! Jocosus2000 (talk) 15:20, 17 September 2021 (UTC)

September 17

Position of black hole event horizon

Is the event horizon (i.e. absolute horizon) of a black hole in the same place for all objects, or does it vary according to their mass or some other factor(s)? PaleCloudedWhite (talk) 07:17, 17 September 2021 (UTC)

The event horizon depends on the mass, charge, and angular momentum of the black hole. Dja1979 (talk) 17:09, 17 September 2021 (UTC)

But is it in the same position relative to all other objects? i.e. if a large planet and a tiny asteroid approach the black hole, would they both cross the event horizon at the same place? PaleCloudedWhite (talk) 17:45, 17 September 2021 (UTC)

As the two objects involved (the black hole and the approaching object) warp spacetime conjointly, the definition of the spatial metric required for a notion of being "in the same place" is tricky. Quoting from Binary black hole § Shape: "As two black holes approach each other, a 'duckbill' shape protrudes from each of the two event horizons towards the other one." (This is observed in numerical simulations based on the GR equations, but there is no reason to assume this mathematical prediction is not faithful.) If the approaching object has a mass that is almost enough to make it collapse into a black hole, continuity implies that the receiving black hole also extends somewhat of an expecting duckbill for its kiss of death. For a planetary mass like that of Jupiter, there must then also be a bump in the shape, but (I suspect) so tiny that it is negligible.  --Lambiam 07:04, 18 September 2021 (UTC)

Thanks. So if your suspicion is correct, any difference would be in terms of degrees of negligibilty. I admit that whenever I try to get my head around the concept of the warping of spacetime, my head starts warping as well....... PaleCloudedWhite (talk) 11:59, 18 September 2021 (UTC)

Getting your head around anything tends to warp it. It stretches the imagination and is a good aid to grokking the Einstein field equations, but take care not to warp your brain into a singularity.  --Lambiam 21:08, 18 September 2021 (UTC)

September 18

If KE generated is tiny due to an object's size, what's the purpose of avoiding it here?

In here it says: The amount of work energy needed to move a unit of electric charge from a reference point to the specific point in an electric field with negligible acceleration of the test charge to avoid producing kinetic energy or radiation by test charge.

If Kinetic energy is due to an object's motion. then an object (in this case, charge) tiny in size, so is necessary to avoid producing KE? Rizosome (talk) 02:54, 18 September 2021 (UTC)

While the mass of the electron is tiny, the velocity and thereby the kinetic energy that an electron can obtain by using an electric potential difference to move them – as is done in particle accelerators used in high-energy physics – can get very large. It can go up to several GeV, a billion times the work of moving an electron around in a low-voltage circuit. The avoidance clause is part of the definition, and is not a matter of a practical set-up for measuring potential.  --Lambiam 06:39, 18 September 2021 (UTC)

How exactly GeV getting avoided here? If it not a matter of a practical set-up, then why it is included in definition ? Rizosome (talk) 04:31, 19 September 2021 (UTC)

The definition (like any definition) describes an idealised situation where the charge is moved infinitely slowly from one point to another. Only in this idealised situation is the difference in potential equal to the work done on the charge. This makes for a clean precise definition, but describes a situation that in practice can only be realised approximately. In any real life situation, the energy balance is more complicated as it has to take into account the difference in kinetic energy and the amount of energy radiated away. Real life is messy, definitions are abstractions that reduce things to the essential aspects. A similar thing happens in thermodynamics, where theory demands that changes of the state of a system occur infinitely slowly so that the system is always in equilibrium. In reality systems always go through non-equilibrium states that are much harder to describe.

Having said that, it seems to me that for the lead sentence of a Wikipedia article this one is rather cluttered. It might be less confusing if that sentence did not mention KE and radiation; the definition could be made more precise further on in the article. --Wrongfilter (talk) 06:41, 19 September 2021 (UTC)

Would a Space probes named after people article be a good idea?

Let me know! 2405:4803:F190:6577:15C3:CAFB:2446:BE2E (talk) 06:41, 18 September 2021 (UTC)

What about using a category? See also WP:CLN and WP:SAL.  --Lambiam 07:08, 18 September 2021 (UTC)

Maybe only if there was also an article on space probes not named for people. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:53, 18 September 2021 (UTC)

More than 70 space probes have been launched, of which only about 10 were named after people. Cassini was named after Giovanni Cassini, Hubble was named after Edwin Hubble, and Kepler was named after Kepler. How many others do you know?  --Lambiam 20:58, 18 September 2021 (UTC)

I count around 25 in List of Solar System probes, though this includes "sub-probes" and some legendary/mythical/fictional "persons." {The poster formerly known as 87.81.230.195} 90.200.67.3 (talk) 05:22, 19 September 2021 (UTC)

That list contains many spacecraft that are still in the planning phase, such as Lucy. (Burning question: Do skeletons qualify as "people"?)  --Lambiam 07:05, 19 September 2021 (UTC)

At this point, Cassini, Kepler and Hubble are likewise "skeletons". ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:39, 19 September 2021 (UTC)

Wouldn't a category suffice? Imagine Reason (talk) 22:21, 18 September 2021 (UTC)

No, we should not create such a category. Per Wikipedia:Categorization "A central concept used in categorizing articles is that of the defining characteristics of a subject of the article. A defining characteristic is one that reliable sources commonly and consistently define[1] the subject as having" This is not a subject that is frequently discussed about space probes. --Jayron32 16:06, 20 September 2021 (UTC)

It is actually fairly common that a news item or communiqué on a space mission such as a probe discusses who it is named for (if anyone):

• With its liftoff, University of Chicago Prof. Emeritus Eugene Parker became the first person to witness the launch of a namesake spacecraft. The Parker Space Probe is the first NASA mission named in honor of a living person.^[1]
• Gavin said the mission was named after Leonardo da Vinci for his Renaissance thinking that went beyond science and art.^[2]
• The Galileo probe, named for the Italian astronomer who discovered Jupiter's four largest moons, orbited the gas giant from 1995 to 2003.^[3]
• The spacecraft was named after John Young, NASA’s longest-serving astronaut, who was an integral part of missions to the moon and the space shuttle program.^[4]
• The names of Octavia Butler, a visionary award-winning writer, and Jakob van Zyl, a brilliant engineer and manager who helped send spacecraft across the solar system, are now part of the Perseverance rover’s mission.^[5]
• The probe was named Huygens, after the person who discovered Titan.^[6]

 --Lambiam 11:30, 21 September 2021 (UTC)

WP:Listcruft says: "In general, a "List of X" stand-alone list article should only be created if X itself is a legitimate encyclopedic topic that already has its own article. "--Shantavira|^{feed me} 08:26, 19 September 2021 (UTC)

Then we have lots of listcruft: List of Asian superheroes, List of Bangladeshi playback singers, List of Chileans of German descent, ...  --Lambiam 11:04, 21 September 2021 (UTC)

Finding examples of people doing the wrong thing is not an endorsement of that wrong thing, you know. --Jayron32 11:13, 21 September 2021 (UTC)

September 19

Ligature in Surgery

Ligature (medicine) has been a stub for more than 15 years, and has only a few lines of content. Is there is corresponding article on surgery which covers this better and so this can be redirected or merged there? Jay ^(Talk) 10:10, 19 September 2021 (UTC)

The nearest I can see is surgical suture. You could discuss possible merger on the relevant talk pages. Each article does "see also" the other. Mike Turnbull (talk) 11:16, 21 September 2021 (UTC)

Yes, I had seen suture, but that article is broader than ligature which is about tying. So I guess, Ligature (medicine) is the only article on enwiki on the topic (which is surprising). Jay ^(Talk) 08:21, 22 September 2021 (UTC)

External v internal pressure

For simplicity, I'll say my lab works with worms. There is a cell underneath the hypodermis that (we think) becomes deformed by either an increase in hydrostatic pressure in the body cavity or by focal compression by objects passing through the body cavity. My coworker is convinced the deformation experienced by the cell can be recapitulated by just increasing the atmospheric (external) pressure. Intuitively I feel uniform external pressure through a homogeneous medium (air), transduced through first a solid but deformable barrier (worm skin) and then through an inhomogeneous fluid (worm guts) is a totally different regime from that of internal hydrostatic pressure or focal compression. My coworker "concedes" that different materials experience different compressibility, but somehow we diverge when it comes to the conclusion of this thought experiment I made up: Say we have a box floating in space (no gravity) with the "top" half filled with air and the "bottom" with water, with or without a solid barrier at the interface; and there is an over-easy egg on a wall in the air half and another on the floor of the water half; if we were to increase pressure by lowering the ceiling (air half) at epsilon increments, would both egg yolks burst at the same time? This is our last dance (talk) 20:57, 19 September 2021 (UTC)

The pressure in the air and water would be identical Greglocock (talk) 00:26, 20 September 2021 (UTC)

Without gravity, why would the water remain in the bottom half? Imagine Reason (talk) 00:54, 20 September 2021 (UTC)

Imagine Reason, I forgot that I needed the impermeable barrier in there. JoelleJay (talk) 04:27, 20 September 2021 (UTC)

If the barrier is flexible enough, its presence makes no difference. But if the moving ceiling reaches the top egg, that one may be first to burst. The forces acting on the worm cell may not be the same in all directions if the deformation is due to non-uniform compression forces, whereas with hydrostatic pressure it does not matter where the pressure comes from.  --Lambiam 05:17, 20 September 2021 (UTC)

The egg yolk is an incompressible liquid surrounded by a fragile membrane and in both cases has force applied equally in all directions ; for very much the same reasons that scuba and free divers eyes are unaffected at depth, neither would burst. 2A01:E34:EF5E:4640:DFC:5965:9101:1BA9 (talk) 16:19, 20 September 2021 (UTC)

Sure. That's why divers don't wear goggles or face masks. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:12, 20 September 2021 (UTC)

You are out of your depth. Yes 2A01, I agree. Thought for Bugs, what is the air pressure in a Scuba divers mask, compared with the surrounding water? Greglocock (talk) 22:22, 20 September 2021 (UTC)

I wouldn't know. But I would like to see a reference for the assertion the IP is making. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:25, 21 September 2021 (UTC)

Divers wear a dive mask because water has a different refractive index to air, not to compensate for hydrostatic pressure (which of course it doesn't; the pressure within the mask is maintained at ambient to prevent barotrauma such as petechial hemorrhage and ultimately exophthalmos due to mask squeeze). I'm really not sure what sort of mystical force you think might be operating unequally upon the yolk membrane to cause it to rupture, so I can't give you a reference for its inexistance (although I can cite the notorious non visual impairment of french scuba diver Jacques Cousteau despite the eleven Kilogram-force per square centimetre exerted on his eyes whilst at 100 metres), but since rupturing clearly involves one part of the surface moving in a different direction to another such that the membrane locally exceeds its elastic limit, you might like to ponder Newton's laws of motion and ask yourself where those opposing velocities come from in a homogeneous medium with only symmetrical pressure forces in play. If any of this is unclear to you, you might like to pose a new, specific, question on the science refdesk. 78.245.228.100 (talk) 05:22, 21 September 2021 (UTC)

Let me add an explicit conclusion to what I wrote above. There are three situations: (A) deformation of a cell due to focal compression; (B) deformation of a cell by hydrostatic pressure in water; (C) deformation of a cell by hydrostatic pressure in air. In (B) and (C) the pressure is isotropic; what matters is the pressure and not the medium through which it is delivered. Since the content of the cell is incompressible, no net force acts on its surface or content (ignoring gravity). So there will be no deformation. In situation (A) also shear stress is at work, giving a different, anisotropic force distribution. The original problem is to choose between (A) and (B). The (B) versus (C) thought experiment does not reflect this problem.  --Lambiam 10:50, 21 September 2021 (UTC)

Ahh I see where some of the confusion lies. By "hydrostatic pressure" in (B) I meant increases in the pressure within the body cavity, which is encased by an elastic membrane and expands into the surrounding tissues with mostly uniform compression (as in, the whole cell would be flattened uniformly). This is in comparison to (A), which involves objects impinging on small sections of the cell. In (C), the whole worm experiences isotropic volume decrease under external hydrostatic pressure, although the stress-strain curve is approximately linear at low stress/strain and then enters a nonlinear strain stiffening regime under larger pressure. So basically there's a limit to degree of compression. Applying negative external pressure produces a comparable stress-strain curve to the linear regime of positive pressure, but without the nonlinear response at increased negative pressures. You are correct that the main issue is the difference between (A) and (B), but I think it's also relevant to understand how the differing biomechanical properties of the internal vs external structures, and the barriers between them, affect their compressibility. In the thought experiment, there should have been a barrier at the air-water interface such that increasing the pressure on the air side by moving the ceiling down would deform the barrier down into the water, but this volume decrease in the water section would not be as much as the volume decrease in the air section. This is our last dance (talk) 20:20, 21 September 2021 (UTC)

September 20

Which reach first at the other end of the cell?

The conventional direction of flow of current is from the positive terminal of the cell to the negative terminal of the cell through the external circuit. But Electrons flow from the negative terminal to the positive through the circuit. So which reach faster at other end of the cell: free electrons or current? Rizosome (talk) 06:32, 20 September 2021 (UTC)

Conventional current is not a real physical flow. It is a mathematical trick traditionally used in circuit analysis that works because things like Kirchhoff's circuit laws work when thought of as electron flow or when we pretend something flows in the other direction. Nothing flows from the positive to the negative. 85.76.72.46 (talk) 07:26, 20 September 2021 (UTC)

That's pretty much the same. Be aware the electric current flow in a circuit is not like a fountain, where water appears and disappears as pumps start and stop. It is rather like piping system of a heating circuit - metallic conductors, making a circuit, are literally full of free electrons ('electricity particles'), same as water pipes are full of water molecules. When you close a circuit (remove an isolating gap) a directed movement of electrons appears - and that is current. Similarly, when you remove an obstacle in a water circuit by opening a valve, water starts to run. Then, of course, there is some time needed for the electrons from one end of a cell to arrive at the other end, just like some time is needed for water molecules pushed from one end of a water pump to arrive at the other end of the pump. However the flow (electric or water current) appears almost immediately in the whole circuit. Additionally, electrons are not distinguishable, so you can not tell when 'the same electrons' come at some point which left some other point some time ago. They have some average velocity which can be determined, but some may move slower and other move faster than that, racing each other. So the question when 'they' (meaning 'precisely the same') reach the other terminal of a cell can not be answered precisely. However the 'mean' flow of electrons reaches the other terminal precisely at the same moment as the current, because that is current. --CiaPan (talk) 10:04, 20 September 2021 (UTC)

There is a flow of traffic from New York to San Francisco, formed by moving cars. Which reaches faster at the other end of the road: the moving cars or the traffic flow? The question is meaningless.  --Lambiam 23:18, 20 September 2021 (UTC)

Actually, it's better conceptualized as the amusement park ride Caterpillar (ride), where there are no "ends". After all, it is an electric circuit. Electrons do move, in a sense, but as you can't actually track the motion of a single electron anyways, thinking about what one does is a meaningless exercise. You can describe the bulk motion of the electrons, what you're looking for there is called the Drift velocity of electrons. In a direct current, there is an example worked out in the drift velocity article. Assume a current I = 1 ampere, and a wire of 2 mm diameter (radius = 0.001 m). This wire has a cross sectional area A of π × (0.001 m)2 = 3.14×10−6 m2 = 3.14 mm2. The charge of one electron is q = −1.6×10−19 C this comes out to 23 micrometers per second; at that speed a hypothetical "electron" (which again, we can't track, but let's pretend we can for demonstration purposes) would travel about 1.38 millimeters in a minute, or 8.3 centimeters in an hour. Electrons move pretty slow. But again, this belies the fact that we can't identify (even hypothetically; it's not a limit of our technology, it is baked into the physics) individual electrons to say where they are going. We can just measure the mass of electrons, and describe how fast the bulk of them moves, on average, statistically. --Jayron32 16:03, 21 September 2021 (UTC)

September 21

Bouncing upwards from walls

In various Super Mario Maker levels I have watched on YouTube, Mario can jump seemingly arbitrarily long distances upwards if he's inside a canyon between two walls, simply by hitting each wall in turn and bouncing off it. Surely this can't be possible in real life, even discounting any damage hitting a wall does to Mario's body? JIP | Talk 02:12, 21 September 2021 (UTC)

Wall jumping is a well established video game tradition. It appears in many games.

But can it be done in real life? Well, obviously nobody can jump four times their own height like Mario does, but could it be done with normal human-scale jumps?

A single wall-jump is a pretty common parkour move, but there are a few YouTube videos that purport to show repeated wall-jumps up a narrow gap. (example) Whether these are real or not is another question. It doesn't seem impossible, but I sure couldn't do it. ApLundell (talk) 03:06, 21 September 2021 (UTC)

The laws of physics allow this. How high a human can jump in a simple jump is determined by the kinetic energy that can be reached at the instant of launch, which is limited by human physiology. In the parkour figure additional energy can be input at each bounce (assuming enough friction), so in principle the athlete can jump higher than they could do in a simple high jump. There is again a limit, but one that is more like the limit in how fast a runner can run (see Running § Limits of speed), where the issue is the delivery of a sustained burst of energy.  --Lambiam 10:21, 21 September 2021 (UTC)

Physics allows it. Suppose the horizontal component of the velocity of the jumper with mass $m$ alternates between $-v_{x}$ and $v_{x}$. At every bounce the jumper exchanges a perpendicular impulse $J_{\perp }=\pm 2v_{x}m$ with a wall. While exchanging this impulse with the wall, there is a normal force acting beteen the jumper and the wall, which allows friction to exchange some impulse in a direction parallel to the wall. This parallel impulse has a magnitude of at most $J_{\parallel ,lim}=2v_{x}m\mu$, with $\mu$ the coefficient of friction. The jumper moves back and forth over a distance of $d$, which is slightly less than the separation between the walls as the jumper has finite size. The time between two bounces is $T={\frac {d}{v_{x}}}$, giving a limiting average vertical acceleration of $a_{lim}={\frac {J_{\parallel ,lim}}{mT}}={\frac {2v_{x}^{2}\mu }{d}}$. As long as $a_{lim}\geq g$, with $g$ the acceleration of gravity, it is possible to climb the wall arbitrarily high (but as exhaustion sets in, your $v_{x}$ will drop). Plugging in some realistic numbers, suppose you can keep your horizontal speed at 3m/s, moving back and forth over 3m (bouncing once per second) and have a friction coefficient of 0.7, you can handle an acceleration of 4.2m/s². That's enough to do this on the Moon, but not on Earth. I guess a proper athlete could do this on Earth though. PiusImpavidus (talk) 10:56, 21 September 2021 (UTC)

• Wall jumping by real people can be done with some difficulty. It is done in parkour and freerunning. See this video for the process one man does to learn the discipline. --Jayron32 15:13, 21 September 2021 (UTC) Ed: Never mind. I'm obviously an idiot. Pay no attention to me. --Jayron32 16:14, 21 September 2021 (UTC)

That's the same video I posted. Except that version looks like it's been copied off youtube, posted on Instagram in a different aspect ratio, then copied off that site and re-uploaded to YouTube. (And re-compressed each time.) ApLundell (talk) 15:18, 21 September 2021 (UTC)

Is it necessary to take bullet out off human body?

In movies, doctors struggle to take out bullets in human bodies. But there is a reality case, where the man lived with a bullet in head for years. Source. Is it necessary to take bullet out off human body? Rizosome (talk) 07:14, 21 September 2021 (UTC)

• Doctors prefer to remove the bullet or bullet fragments, as they could cause infection or other trouble. They may elect to leave one in if the procedure to remove it is more risky than leaving it in. This is commonplace, and sometimes the bullet works itself out of the body on its own, like a splinter. Abductive (reasoning) 09:32, 21 September 2021 (UTC)

(ec) Sometimes it's too dangerous to try to remove them, e.g. They Survived Mass Shootings. Now They Are Living With Bullets Inside Them. (The New York Times), They Survived Mass Shootings. Years Later, The Bullets Are Still Trying to Kill Them (lead poisoning, Time) Clarityfiend (talk) 09:40, 21 September 2021 (UTC)

More on lead poisoning. https://pubmed.ncbi.nlm.nih.gov/8057396/ 41.165.67.114 (talk) 12:09, 21 September 2021 (UTC)

Did we just assume bullets are made of lead? 67.165.185.178 (talk) 12:56, 21 September 2021 (UTC).

They often are. But regardless of what they're made of, they're unlikely to be sterile when they enter the body. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:05, 21 September 2021 (UTC)

We believe that in GSW [gunshot wounds] of the spine, retained bullets do not increase the likelihood of septic complications. [7] Alansplodge (talk) 14:21, 21 September 2021 (UTC)

There are no standard medical guidelines regarding bullet removal and the full extent of the consequences of RBF [retained bullet fragments] remains unknown... Meta-analysis demonstrated BLL (blood lead level) significantly higher in individuals with RBF as compared to controls. [8] Alansplodge (talk) 14:21, 21 September 2021 (UTC)

• Theodore Roosevelt carried a bullet inside him for the last seven years of his life, after his failed assassination attempt. -- Jack of Oz ^{[pleasantries]} 22:22, 21 September 2021 (UTC)

That's a lie! Every person Teddy tried to eradicate ended up dead. Clarityfiend (talk) 10:35, 22 September 2021 (UTC)

September 22

Measure oxygen concentration

I want to test an oxygen concentrator for purity of the oxygen coming out. Any idea how to do that? It gives a slow, low pressure stream of oxygen coming out of a tube. Holding a lit match near the output makes the flame flare up a little, but it's not dramatic. Is there another simple test? Thanks. 67.164.113.165 (talk) 03:21, 22 September 2021 (UTC)

I once worked for a company where there was an instrument that measured that, for O2 and CO2. It had a thin needle to measure, and ran for a few seconds, then outputted a number. They said the instrument was worth $5,000. Maybe you can search on-line for such an instrument, but I'm not the right person to help get you started. 67.165.185.178 (talk) 07:50, 22 September 2021 (UTC).

A hand-held scuba nitrox analyser will give you the Oxygen fraction to within about 0.1% and you can probably find one for around €120. If you're handy with a soldering iron you could make your own for a fraction of that. 2A01:E34:EF5E:4640:A028:DB79:13E4:2403 (talk) 12:20, 22 September 2021 (UTC)

The article that discusses the equipment is oxygen analyser. There seems to be plenty of choice. Mike Turnbull (talk) 15:07, 22 September 2021 (UTC)

Those are indeed the general type of equipment. The specific analysers shown in the article are trimix analysers which also measure the fraction of helium, making them much more expensive creatures though. As discussed in the article, the underlying principle is to measure the current output of a galvanic cell across a load resistor, so if you're not too worried about high precision you can just use a voltmeter. 2A01:E34:EF5E:4640:A028:DB79:13E4:2403 (talk) 15:16, 22 September 2021 (UTC)

Making steel from Fe(II) instead of Fe(III).

Steel is currently Fe(III). What would be the problem for trying to make steel from Fe(II). Need a counter-anion? Sure, then make a counter-anion. Would that work? What would be the problem for trying to make steel from Fe(0) to Fe(II)? 67.165.185.178 (talk) 07:52, 22 September 2021 (UTC).

Steel is not Fe(III). I'm not sure where you got that from. Steel contains atomic iron, Fe(0) if you will. It is an alloy of iron and carbon and sometimes other trace metals. Alloys are not ionic compounds, they are elemental mixtures. The rest of your question cannot be answered because it was based on a false premise. --Jayron32 12:01, 22 September 2021 (UTC)

On the other hand, steel ultimately comes from iron ore and as that article suggests some of the ore is indeed Fe(II) (for example siderite) while others are Fe(III) (for example hematite). Whatever the ultimate source of the iron, the process involves chemical reduction to Fe(0) by smelting or direct reduction. The standard reducing agent is carbon, normally in the form of coke, as this is cheap and readily available. A proportion of the carbon may be left in the iron, forming steel. Mike Turnbull (talk) 14:59, 22 September 2021 (UTC)

Sneezing into a respirator

After an open-mouthed sneeze into a respirator, does it need to be replaced right away or at the end of the day? Thank you. Imagine Reason (talk) 12:57, 22 September 2021 (UTC)