October 21

Is it possible to get a(n) (almost) ternary ideal solution/mixture from two non-ideal binary mixture with different sign of deviation from ideality: one binary with negative deviation and the other with positive deviation so that the opposite sign cancel each other, thus producing a practically ideal ternary solution? What properties of mixtures data is available for this possibility? (Thanks!)--82.137.11.130 (talk) 21:50, 21 October 2017 (UTC)[reply]

Generally, you would have to consider the deviation from ideality of all 3 binary pairs, so that ΔH_AB + ΔH_BC + ΔH_AC = 0, though there are probably nearly ideal binary solutions where one of the enthalpies of mixing can be ignored. I'm not sure that what you propose is possible, but here are some references that might get you started (with a lot of work) from a mathematical angle: this [1] from here [2] talks about the thermodynamics of non-ideal solutions and what some of the non-ideal terms mean. This [3] briefly extends the concepts to ternary solutions. This [4] (mostly behind a pay wall) discusses mathematical modeling of non-ideal ternary solutions. Between them, you might be able to get a good idea of what causes non-ideality and how to counteract it.

Solution thermodynamics applies to the solid state as well as the liquid, and is a fundamental study in the field of metallurgy, and more generally materials science (see for example the examples from geology above). Textbooks on metallurgy will have entire chapters devoted to it.

Regarding your second question, there are tables of enthalpies of mixing and heats of solution. Perry's Handbook for Chemical Engineers, 7th Edition, table 2-224 pp.2-201 to 2-203 lists some heats of solution of inorganic compounds.

There may be a much simpler answer to your question, say an example of where this has been accomplished, or at least tried, but so far I haven't found it.--Wikimedes (talk) 22:19, 22 October 2017 (UTC)[reply]

October 22

How does a battery operated clock with a pendulum keep the pendulum swinging? I'd like to make something that will keep swinging but keep the mechanism small so it mustn't have any of that nonsense pertaining to time keeping. 185.81.136.19 (talk) 09:16, 22 October 2017 (UTC)[reply]

An Escapement is the way a pendulum is kept swinging to compensate for slowing due to friction. DMacks (talk) 09:28, 22 October 2017 (UTC)[reply]

That's the mechanical method, but are not electromagnetic pulses more common in battery clocks? (Reference needed.) Dbfirs 09:50, 22 October 2017 (UTC)[reply]

• There are (at least) two ways:

The simplest and cheapest way for a clock is to have a battery powered clock mechanism, with a pulse motor driven by a quartz clock circuit. This ticks once per second (or twice that). A pendulum is attached and is 'pumped' by the motor, via the clock mechanism. The Q of the pendulum system is very low, so the system is able to run at a frequency far lower than the natural frequency of the pendulum, as the purely decorative pendulum is often far too short. The pendulum plays no part in the timekeeping.

An older version of this was used in cheap spring-wound cuckoo clocks, which used a balance wheel escapement to control timing, but also had a decorative pendulum. Those often needed to have the pendulum manually adjusted to be approximately in synch, otherwise they could run very unevenly.

A different approach is a pendulum that does the timekeeping (as a pendulum) and is driven by a magnetic arrangement. These are very common today, not as clocks but as solar-powered "dancing flowers" (We ought to have an article on these, they have some neat mechanisms). In these, there are two coils in the base, and a magnet on the pendulum. As the magnet swings past the coil, the "sense" coil detects it (a small current is induced in the coil). This triggers the circuit, which is a simple amplifier and which then puts a pulse through the larger "drive" coil, which accelerates the magnet in the pendulum and kicks it. The feedback and timing is controlled entirely by the mechanical pendulum. Andy Dingley (talk) 11:21, 22 October 2017 (UTC)[reply]

Thanks for that excellent explanation, Andy. My battery-powered clock has a quartz oscillator for timekeeping, and a completely independent magnetic pulse circuit to drive the "pretend" pendulum. The clock works with the pendulum stopped. Dbfirs 12:12, 22 October 2017 (UTC)[reply]

I did see a clock a while back which was like a big grandfather clock and had a complicated looking pendulum to compensate for the temperature. It operated off a car battery I think and had wires from it so it could drive secondary clocks elsewhere in time with it. I found [5] which describes something very like it. It hhad a display but I'm not altogether certain it was connected to the pendulum, it might have been a slave clock. Dmcq (talk) 15:11, 22 October 2017 (UTC)[reply]

Was it a Master clock? There are lots still working near to where I live. Dbfirs 16:59, 22 October 2017 (UTC)[reply]

Yes that does describe it well. I had multiple rods in the pendulum rather than the simple looking ones in the article but I guess there must have been quite a number of types. Dmcq (talk) 17:48, 22 October 2017 (UTC)[reply]

A master clock is almost the opposite of what we were discussing here. It's an old idea for a mechanical pendulum clock, controlled by the pendulum's mechanical timekeeping, which then operates switch contacts and in turn drives a number of other clocks. The pendulum clock also electrically powers itself, but this is (like the dancing flowers) just a power amplifier, not a timing regulator. The slave clocks are electrically powered and very simple.

These were found in many telephone exchanges, where they would then drive clocks throughout the building and beyond. They often drove tower clocks (clocks in towers) because this made the clock in the exposed position much simpler and more reliable, keeping the sensitive parts closer to hand. For accuracy they usually had long pendulums but only rarely a gridiron pendulum for temperature compensation. It was more usual to have them themselves synchronised to a more accurate master clock (usually Greenwich), and those clocks would have an automatic synchronising mechanism (a "heart-shaped cam") as well. Andy Dingley (talk) 19:24, 22 October 2017 (UTC)[reply]

Another option is to just keep the pendulum mechanism entirely unpowered and unused for time-keeping. That is, it can use weights to run the pendulum, but not use the pendulum for anything. Thus, you could have the accuracy of a quartz clock with the "old-timey" feel of a pendulum. You could let the pendulum run down, when nobody is around to impress by it, rather than have it use up batteries. Then set the weights when company is coming over. StuRat (talk) 22:08, 22 October 2017 (UTC)[reply]

... only if the guests are making a very short visit! Dbfirs 00:01, 23 October 2017 (UTC)[reply]

A low friction pendulum should be able to continue for several hours, at least. See Longcase_clock#Description, which mentions an 8-day mechanism and a 30-hour mechanism. This one is supposedly on the small side, with corresponding reduction in run time, but shouldn't expend any pendulum energy moving the hands or chiming, which should make it last longer. StuRat (talk) 00:05, 23 October 2017 (UTC)[reply]

No, that is not an example of an unpowered pendulum. Those pendulums are driven by weights and have escapement mechanisms. I suggest you try an undriven pendulum yourself to see how long it lasts. Apologies if I misunderstood your suggestion. I do like your idea of having an accurate quartz mechanism for timekeeping but retaining the weight-powered pendulum for effect. Dbfirs 07:04, 23 October 2017 (UTC)[reply]

I meant unpowered by electricity. Weights are exactly what I had in mind. Sorry if I was unclear. Electricity to drive the quartz clock, and weights to drive the pendulum, and no interaction between the two. StuRat (talk) 03:38, 25 October 2017 (UTC)[reply]

I would like to make a steamer for wood bending and I've read that a PVC pipe (like a drain pipe?) can be used as a vessel for this but I need a conduit to convey steam from my kettle on the gas stove to my PVC pipe. What would be a suitable but cheap material for such a conduit? How hot is it likely to get? I figure no more than 150 °C? --178.170.142.48 (talk) 22:50, 22 October 2017 (UTC)[reply]

To clarify, do you mean to convey the steam under pressure, or just at normal atmospheric pressure ? StuRat (talk) 23:01, 22 October 2017 (UTC)[reply]

Yes, the pressure would only be slightly higher than atmospheric. 23:27, 22 October 2017 (UTC)

If you design it like this one you don't need any conduit: [6] The steam box sits directly over the steam source. Rmhermen (talk) 23:17, 22 October 2017 (UTC)[reply]

Meaning directly over the kettle ? StuRat (talk) 23:22, 22 October 2017 (UTC)[reply]

I think that would just shift my problem somewhere else. I'd need to find a way to perch my wood container over the source of the steam in such a way as to capture it efficiently (and I don't wish to make a heater when I can just use my gas stove). --178.170.142.48 (talk) 23:27, 22 October 2017 (UTC)[reply]

This one uses a PVC pipe and a garden hose: [7] Rmhermen (talk) 23:21, 22 October 2017 (UTC)[reply]

• Plain old PVC should work just fine, because that steam cannot be much hotter than boiling. However, if you want a conservative design, you can use CPVC instead for the conduit. CPVC is normally used instead of PVC for hot water under pressure. If you are truly paranoid, use a copper or stainless flex pipe of the type sold to connect a hot water heater to the house plumbing. -Arch dude (talk) 03:09, 23 October 2017 (UTC)[reply]
  • If you find that the steam is losing too much heat and/or condensing in your pipe, hardware stores also sell closed-cell insulation that goes around hot water pipes. --Guy Macon (talk) 03:45, 23 October 2017 (UTC)[reply]

• My steam bender is made from a scrap offcut of large diameter plastic underground gas pipe, the yellow plastic stuff. The steam is supplied by one or two wallpaper steamers. These are cheap (as cheap as a kettle), larger water capacity and already have a hose attached. You should avoid steel in making such a steamer - especially if you're working oak or chestnut - as there is a risk of blue-black or rust staining if iron is combined with the tannates inn the wood.

Generally any sort of flexible plastic pipe from a typical plumber or electrician will do. Lots of people use 20mm flexible electrical conduit, which is usually PVC. Andy Dingley (talk) 09:59, 23 October 2017 (UTC)[reply]

October 23

I want to know, outside of Germany, are the flying insects disappearing? Do old people remember there being more flying insects in their youth than there are today? 110.22.20.252 (talk) 03:54, 23 October 2017 (UTC)[reply]

Yes. Bugs are declining. http://www.telegraph.co.uk/science/2017/08/26/windscreen-phenomenon-car-no-longer-covered-dead-insects/ 196.213.35.146 (talk) 07:31, 23 October 2017 (UTC)[reply]

I assume you excluded Germany because you've already seen this: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0185809 196.213.35.146 (talk) 08:28, 23 October 2017 (UTC) [reply]

Given the huge increase in vehicular traffic and the general increase in speed it should come as no surprise that there will be a decrease in flying insects. I'm in my 7th decade and I remember in the English countryside when you would look up if a car was approaching, and you could sit at the roadside, the A30, than a major trunk road, and write down vehicle registration numbers (for later sorting and scrutiny) with sometimes 10 or 15 minutes between vehicles. Ah, those days. Richard Avery (talk) 14:29, 23 October 2017 (UTC)[reply]

In case it's not clear: the decline is not due to vehicle use per se, that's just how some people notice the fact. The decline in flying insects is associated with pesticide use, habitat loss, habitat degradation, habitat fragmentation, and climate change. SemanticMantis (talk) 14:53, 23 October 2017 (UTC)[reply]

OP and interested parties should look through the first few paragraphs of that paper, and the first ~30 or so references, many of which document the decline of flying insects in other parts of the world. It's not just Germany, it's fairly widespread around the world. SemanticMantis (talk) 14:53, 23 October 2017 (UTC)[reply]

Notwithstanding the risibility potential of malodorousness heralded by audible signal due to sudden decompression of postprandial gaseous abdominal distension, this involuntary occurrence is neither a respectful nor a unique designator of persons of advanced maturity, for whom such usage as that in the heading should be deprecated. Blooteuth (talk) 15:52, 23 October 2017 (UTC)[reply]

So, if the spiders can't eat as many insects as they were used to will they turn on us? :) . Count Iblis (talk) 22:32, 23 October 2017 (UTC)[reply]

I've personally killed some 500 box elder bugs in my house this fall (one 30 seconds ago), so I have to think human population has an effect. StuRat (talk) 23:40, 23 October 2017 (UTC)[reply]

What "fun science" can I demonstrate to kids, about 10 to 14 years old, using a red (650nm) laser pointer and common household objects and substances? Roger (Dodger67) (talk) 10:22, 23 October 2017 (UTC)[reply]

I always thought prisms were cool. Refraction demonstrations maybe? 196.213.35.146 (talk) 10:44, 23 October 2017 (UTC)[reply]

Diffraction has a demonstration using a red laser. 196.213.35.146 (talk) 10:49, 23 October 2017 (UTC)[reply]

• Before you switch the laser on, ask them what they expect the beam itself to look like. Then show them it's invisible when passing through air. Cue discussion about Star Wars physics? Then make the beam visible by producing smoke in its path, or splashing some flour or whatever.
• Try diffracting the beam through an empty drinking glass by pointing it to the glass off-centre, and mark where the beam lands on a sheet of vertical paper. Test what happens when you fill the glass with water.
• Have the students predict what colour the spot will appear when the laser is shone on white, black, red, and green objects.

Adrian J. Hunter^{(talk•contribs)} 10:58, 23 October 2017 (UTC)[reply]

• I have a handy gadget, which started out as expensive school kit but can now be made at home with a few bucks on eBay. A small plastic box to hold the batteries and a switch, with a red laser module mounted in the side of it. But rather than the usual laser pointer, this has a line lens on it, to give a vertical plane of light, relative to the box base.

The advantage is that you can place this on a sheet of paper and demonstrate mirrors, prisms, lenses etc. and because the light is a plane rather than a line, it's visible as a path right across the paper. It makes ray tracing far simpler.

A purple laser also shows interesting fluorescence effects, on materials like hardwood, uranium glass and the usual fabrics washed in optical brighteners. Andy Dingley (talk) 11:39, 23 October 2017 (UTC)[reply]

• This has some suggestions. --Jayron32 11:56, 23 October 2017 (UTC)[reply]

• One quick thing they might find interesting is to learn that their skin is somewhat transparent. Turn the lights out at night, and have them hold up their hand, then shine the laser pointer through the webbing between the thumb and the rest. The red light travels well through thin skin, so they should see a nice red glow on the other side. I would insist on handling the laser pointer myself, though, so they can't shine it in each other's eyes, potentially causing damage. If this has to be done during the day, use a darkened room or even put hand under a box. (You might be able to see some red light shine through in full light, but it won't be nearly as impressive.)
• You could use this as a talking point to lead into how we are even more transparent to other types of radiation. Also, if your kids have a mixture of skin colors, they might notice that dark-skinned people are less transparent to light. This can lead to a discussion of melanin and how it evolved to protect from UV light, and how this also limits vitamin D production from sunlight, so isn't as prevalent in places with little sunlight. See Vitamin_D#Synthesis_in_the_skin. StuRat (talk) 17:47, 23 October 2017 (UTC)[reply]
• My apologies if it's already been mentioned, but I always thought the laser pouring water experiment was cool, it simulates the total inner reflection which explains how fiber optics work. Anywho the video is here, enjoy! Drewmutt (^ᴥ^) talk 00:11, 24 October 2017 (UTC)[reply]

P.S. Depending on how intense you're lil' guys are there's some easy Double-slit experiments you can do at home to demonstrate quantum mechanics. It's easy to do and the instructions are here. Drewmutt (^ᴥ^) talk

• Please teach laser safety first. -Arch dude (talk) 02:23, 24 October 2017 (UTC)[reply]

No, don't try to teach laser safety. It's far too complicated. Instead, limit all exposure to devices with a strongly divergent beam that are inherently eye-safe. Don't have anything around that you can't safely catch an eyeful of, because it _is_ going to happen. Andy Dingley (talk) 15:33, 24 October 2017 (UTC) (using class 4s since thirty-odd years ago)[reply]

• This is why I suggested that only the adult should actually handle the laser. Teaching laser safety is fine, but I wouldn't trust kids with lasers any more than I would trust them with guns (and I don't live in a red state, so we don't have any UZI-packing 9-year-old girls: [8]). StuRat (talk) 16:14, 24 October 2017 (UTC)[reply]

• my daugther (aged 14 then) made a Michelson interferometer using a laser, some fixed mirrors, a half-silvered beam splitter, and one mirror that moved using a piezo element. the cool part was that she could demonstrate that the diffraction pattern varied as the piezo moved, showing that she could measure movements down to a few percent of one wavelength of red light (about 10 nm). Her piezo element was the driver from the inside of a buzzer. iI cost about a dollar. she drove ti with a 9-volt battery and a potentiometer. the only expensive part was the half-silvered mirror. -Arch dude (talk) 02:23, 24 October 2017 (UTC)[reply]

Thanks everyone for the great ideas. I'll certainly keep safety the first priority. The laser I'm using is a "Class III" 5 mW at 650nm. Roger (Dodger67) (talk) 18:59, 24 October 2017 (UTC)[reply]

In the chemistry section of the pyrethrin page Cinerin II and Jasmolin II are related compounds which differ by the addition of a single methyl group yet Jasmolin II has >7,000x the solubility in water. What accounts for this difference? The methyl group is not polar, if anything I would expect a longer carbon chain to reduce solubility in water not increase it. 208.90.213.186 (talk) 21:30, 23 October 2017 (UTC)[reply]

Is there any research on the cognitive abilities of seagulls? About how well do they compare to corvids and other famously smart birds? My impression is that they're fairly smart, if not corvid level. For example, they can apparently learn to recognize and open food packaging. 2607:F720:F00:4846:1470:AFDA:7A5F:98B5 (talk) 22:00, 23 October 2017 (UTC)[reply]

Unfortunately, our resident seagull expert, @Kurt Shaped Box:, seems to have retired. You might leave him a note on his talk page, though, in case he returns. StuRat (talk) 22:17, 23 October 2017 (UTC)[reply]

One way to compare animal intelligence is the mirror test. StuRat (talk) 23:43, 23 October 2017 (UTC)[reply]

Anecdata: I've often seen gulls trying to attack their reflections, so they evidently don't pass the mirror test. 169.228.159.252 (talk) 03:09, 24 October 2017 (UTC)[reply]

Not necessarily. They might figure it out, given time. Heck, a person seeing their reflection in a mirror in an unfamiliar, darkened room might be startled, until they figure it out. StuRat (talk) 03:16, 24 October 2017 (UTC)[reply]

Maybe they're expressing angst. InedibleHulk (talk) 03:19, October 24, 2017 (UTC)

• Seagulls do routinely drop shelled items to feed, there are many videos at youtube. But other than be aggressive and trying to eat anything? I can find no evidence of tool use, co-operative behavior, or cleverness at picked locks. Of course that's absence of evidence. μηδείς (talk) 02:20, 24 October 2017 (UTC)[reply]

• Incidentally, they may not actually recognize food packaging. There could be several other explanations for why they open them:

1) The see food through clear packaging.

2) They smell food through the packaging.

3) They just open similar packaging, on the hope that it contains food. The test here would be if they open non-food packaging of the same size and shape. If so, that means they just try them all. StuRat (talk) 02:55, 24 October 2017 (UTC)[reply]

That's a fixed action pattern which is the opposite of intelligence. It serves the gull well often enough that it's an evolutionarily stable behavior. The same can be said of Sand Wasp reproduction. Again, I am not saying there's evidence gulls are stupid. But "they just try them all" is no evidence of their intelligence. μηδείς (talk) 05:48, 24 October 2017 (UTC)[reply]

Yes, and we need to avoid anthropomorphization. An example I like to use is that if a human community has one well dry up, they may move closer to the remaining working well, using their intelligence. A plant will also "move" closer to it's one remaining water source, in that roots and stems nearby will enlarge while roots and stems further away will whither, but this doesn't mean any intelligence was involved. StuRat (talk) 16:24, 24 October 2017 (UTC)[reply]

There's also no stupidity involved when a sunflower "stares" at its photons. Deep down, I think most of us know this, but many still insist these dolts put on the glasses. Even if intended as a public relations boost, not UV protection, the whole altruistic idea us is based on a misconception. They don't give a f**ge about us, whether farmed like docile cattle or growing free and wild in a ditch somewhere. We would be in a sorry state without their essential oil. We can't shake their hands, pat their backs or kiss their feet, but we can at least not (physically) disturb them while they're busy doing the job we couldn't do as well and would rather not at all. InedibleHulk (talk) 03:47, October 25, 2017 (UTC)

I'd still like to try my idea of placing small solar panels on sunflowers, to let them to the sun tracking for us. Who needs expensive machinery for that ? StuRat (talk) 03:53, 25 October 2017 (UTC) [reply]

October 24

In File:Nucleosynthesis periodic table.svg this graphic, elements 43, 84-88, and some others are a color that doesn't match anything in the legend. Where do these come from? Bubba73 ^{You talkin' to me?} 05:29, 24 October 2017 (UTC)[reply]

The brown/tan-ish color is "100% synthetic", according to the popup notes when hovering over those elements as the image description recommends. I agree the legend is deficient, and SVG-implemented image annotations are not as standard as the ImageAnnotator gadget. DMacks (talk) 05:35, 24 October 2017 (UTC)[reply]

Thanks, the SVG works but I had converted it to a PGN. Synthetic radioisotope helps. Bubba73 ^{You talkin' to me?} 13:59, 24 October 2017 (UTC)[reply]

During a fire, can you still breathe when a halon fire extinguisher is activated? Or is it expected to aerate the room (train/plane) immediately after halon is used?--Hofhof (talk) 23:24, 24 October 2017 (UTC)[reply]

Neither. All people are expected to evacuate the room immediately. Only when firemen declare it safe should the air be exchanged and the room reoccupied. StuRat (talk) 23:35, 24 October 2017 (UTC)[reply]

And what if the fire is inside a plane or train? --Hofhof (talk) 23:48, 24 October 2017 (UTC)[reply]

Then you don't use halon. You would stop the train immediately and evacuate, or evacuate to other cars. A major fire on a plane in flight is rather deadly, as there aren't many good options for dealing with it. Prevention is the usual course of action. For a small plane fire, usually just a smokey smell, they also land as soon as possible and evacuate. StuRat (talk) 02:12, 25 October 2017 (UTC)[reply]

Aircraft are one of the few exemptions where you will still find halon. Andy Dingley (talk) 02:54, 25 October 2017 (UTC)[reply]

• Depends on the halon. They're all asphyxiants, but halons (unlike CO₂ flood systems) are primarily a chemical agent. So they're used in smaller concentrations than CO₂. Halon 1301 was the favoured agent for flood systems, halon 1211 for hand-held extinguishers. Both are considered somewhat toxic and exposure should be restricted, and 1301 was favoured for flooding as it was somewhat safer. They are though safe enough that people can escape a space that has been flooded.

Halon is no longer used for fire extinguishers, except in some very narrow exceptions, owing to concerns over ozone depletion with CFCs (bromine compounds like the halons too). Halons are still used in some rare situations (I think WP was recently saying that they were completely banned, and there was edit-warring over this) - the Channel Tunnel is one. Flood systems have largely been replaced with CO₂. Halotron I is a non-ozone-depleting replacement for halon 1211 in hand-held uses and has similar toxicity - exposure should be limited, but it's better than being in a fire.

Older agents, notably carbon tetrachloride or Pyrene fluid were remarkably effective extinguishers, but quite evil for toxicity in confined spaces. They're chronically liver toxic for exposure to the fluid and acutely extremely toxic if the fluid is sprayed onto a fire, as phosgene is produced. This was particularly hazardous in sealed spaces, such as tanks - Pyrene extinguishers were fitted to them for a long time, then later only fitted externally. Even smoking near a spill of the fluid has been known to be immediately fatal. Andy Dingley (talk) 00:11, 25 October 2017 (UTC)[reply]

October 25