Wikipedia:Reference desk/Archives/Science/2015 February 3

= February 3 =

Sulfate calcination
Is there a substance which lowers the calcination temperature of anhydrite? Plasmic Physics (talk) 03:13, 3 February 2015 (UTC)

Non-visible paint ?
For obvious reasons paint comes in colours (UK spelling) on the visible spectrum. But is it possible to produce paint with a colour beyond the visible spectrum ? (though I guess colour may be the wrong word) if so then what colour would such paint appear to the eye ? would it appear different if just off the red compared to the violet end ?

I suspect the answer is, yes, black and no respectively, but thought I'd check here ! GrahamHardy (talk) 10:13, 3 February 2015 (UTC)
 * Interesting point. For fun, I just googled 'infrared paint'. It returns pictures too ;-). -DePiep (talk) 10:51, 3 February 2015 (UTC)


 * The color something appears to be has to do with which spectral lines reflect. So there's a fair chance that ordinary paint reflects various infrared and/or ultraviolet wavelengths. In short, we already have it - you just can't tell by looking at it. ←Baseball Bugs What's up, Doc? carrots→ 11:09, 3 February 2015 (UTC)


 * Try googling "invisible paint" and "black light paint" for more examples. Gandalf61 (talk) 12:33, 3 February 2015 (UTC)


 * For WP references, see line of purples, impossible color, spectral color, and just for fun, list of fictional colors. SemanticMantis (talk) 14:18, 3 February 2015 (UTC)


 * "black light paint" is something different. That's paint that absorbs UV light and re-emits it into the visible spectrum.  Many materials do that.  They let you see where UV light is shining, but you're not "seeing" UV - the colors you see are in the regular part of the spectrum.  Paint like that probably doesn't reflect much UV at all.  It's kinda the opposite of what our OP is asking about.  SteveBaker (talk) 15:47, 3 February 2015 (UTC)


 * All paint reflects some light outside of the visible spectrum - some more than others - so any color of paint is reflecting some light that we can't see. But if you're asking for paint that ONLY reflects IR or UV or something, then such a "color" would appear black to our eyes.  Black paint can be made to reflect strongly in either the IR or UV - but generally it's poor at doing so in the regions of IR and UV close to the visible spectrum.  Sadly, nothing very exciting happens...the paint just looks black.  You can tell the difference though if you use a pair of night-vision goggles that reacts to IR light.  It's interesting to view the world through a pair of those because it opens up a world of "color" (albeit in shades of green) that we can't usually see.  I vividly recall looking at an american flag and noticing that the red and white stripes looked the same - only the blue corner with the stars on it was distinctive.


 * Also, if you know someone who had cataract surgery more than about 10 to 20 years ago, they had part of their eye removed that filters out some of the incoming UV light. My mother is one of those people.  They are actually able to see a little way into the ultra-violet.  A rare genetic condition can also prevent that part of the eye from developing - and those people can naturally see a little UV light.   These people don't get the perception of entirely new colors - UV just looks like blue or a blueish purple to them.


 * My mom is an enthusiastic gardener and reports that after her surgery, she could see very subtle spots and stripes on some flowers that she'd never noticed before - and that these subtle markings 'go away' when she wears her glasses (which, presumably, filter UV light). It turns out that some flowers have UV-reflective markings to help to guide bees in to land on them - rather like the markings we paint on airport runways.  Since bees see in the UV, this makes quite a bit of evolutionary sense.  To our normal eyes, those markings are the same "color" as the rest of the petals.


 * Modern cataract surgery avoids doing that because the additional UV exposure can damage your eyes - so people who had the surgery recently lack my mom's "super power".


 * SteveBaker (talk) 15:44, 3 February 2015 (UTC)


 * The paint could appear any color to the human eye. There's no reason in principle why you couldn't make a paint with some particular infrared reflectivity spectrum, and whatever visible spectrum you like. Obviously if the paint has to reflect infrared light that is close to the visible spectrum, it will likely also reflect at least some red light too so there would be a smaller range of possible colors. In principle, you could certainly make paint that reflected infrared but was transparent in the visible.--Srleffler (talk) 18:32, 3 February 2015 (UTC)


 * I can envision a theoretical use for paint that reflecs IR or UV in addition to a visible color: encoded messages or images. Say you paint a wall with blue paint. Then you paint an image on the wall that reflects both blue and IR. Using night-vision goggles, the image invisible to others would be visible to you. Or did I just say something foolish?  → Michael J Ⓣ Ⓒ Ⓜ 11:29, 5 February 2015 (UTC)
 * I think this would be less secure than paint that takes UV light and makes it visible, since night vision goggles would be more likely in a situation where... you would be using night vision, if you get me. Also it'd show up on crap cellphone cameras since they don't have UV filters, I think. There's no reason it wouldn't work though.81.138.15.171 (talk) — Preceding undated comment added 14:38, 6 February 2015 (UTC)

What's the tougher technical problem for using hydrogen fuel in a car?
Wouldn't hydrogen be a better energy storage medium that those batteries that electric cars use? --Noopolo (talk) 14:49, 3 February 2015 (UTC)
 * Here are several articles about the technical hurdles for running cars on hydrogen fuel cell technology. -- Jayron 32 14:58, 3 February 2015 (UTC)


 * Hydrogen poses many problems if you try to use it in an internal combustion engine - mainly that it rapidly makes most metals that it touches very brittle - so engine reliability goes down the toilet and you have to make your engines out of exotic plastics and ceramics. However, you can use hydrogen in other ways - such as in a fuel cell that can generate electricity directly and thereby charge batteries and drive an electric vehicle.  That avoids most of the problems, but it still technically challenging.   Dispensing hydrogen is also a problem, it's tough to liquify (compared to fuels like propane) - so it has to be delivered as a highly compressed gas, which makes refueling difficult.   Storing the stuff is also tricky - those teeny-tiny molecules can sneak past most kinds of seal that you'd want to use.  It's also much more explosive and inflammable than gasoline - so you can have car crashes of hindenburg-like proportions.  There are many practical difficulties.  The other issue is that hydrogen doesn't occur naturally - it has to be manufactured - typically by electrolysis of water.   That's an inherently inefficient process.   Electricity=>Hydrogen=>Electricity is clearly a less efficient process than Electricity=>Battery=>Electricity.


 * SteveBaker (talk) 15:25, 3 February 2015 (UTC)
 * The advantage of electric vehicles is you can simply drop them into the existing energy distribution infrastructure: plug them into electrical sockets, or stick a generator in them to burn existing, readily available fuels, or both, as with plug-in hybrids. Hydrogen vehicles require an entirely new hydrogen infrastructure, plus all the other issues listed above. Market effects should not be underestimated when evaluating how successful new technologies may be; a lot of companies have made that mistake and it cost them. --71.104.75.148 (talk) 23:27, 3 February 2015 (UTC)


 * Forget hydrogen, it's a pain in the butt. You are much better if you turn Hydrogen into Methane. Methane is much easier to store and to use. Or better still turn it into Hexane. All you need is some carbon atoms. Hexanes are significant constituents of gasoline. Hexane is a colorless liquid at room temperature, odorless when pure, with boiling points between 50 and 70 °C. They are widely used as cheap, relatively safe, largely unreactive, and easily evaporated non-polar solvents.175.45.116.65 (talk) 04:19, 4 February 2015 (UTC)


 * Add two more carbon atoms and make octane. But hydrogen as a burnt fuel isn't practical for energy density reasons and the source for hydrogen is petroleum (even though water could be the source, it's too expensive.)  Electric cars only make sense if the power plant is clean.  The problem is that the "gas tank" takes hours to fill, wears out, and costs thousands of dollars to replace.  Batteries aren't anywhere near the energy density of gasoline.  --DHeyward (talk) 14:51, 4 February 2015 (UTC)


 * The problem with Methane is that it's a horrible greenhouse gas...and burning it makes CO2 - which is precisely what we're trying to avoid here. So attaching carbon atoms to your hydrogen *completely* nullifies the entire point of doing this in the first place! SteveBaker (talk) 20:12, 4 February 2015 (UTC)

We do have an article Hydrogen fuel but unfortunately a lot of it is unreferenced. Richerman   (talk) 20:22, 4 February 2015 (UTC)

Sun
When the Sun provides its heat, does it provide smoke along? From all the colours it is known of? -- (Russell.mo (talk) 19:56, 3 February 2015 (UTC))
 * Does the sun provide smoke to the Earth? No. The heat from the sun is not from a smoke producing combustion reaction to begin with, but rather from nuclear fusion. Can you clarify what you mean by the last part of your question, regarding colors? --OuroborosCobra (talk) 20:49, 3 February 2015 (UTC)
 * Only if you expand the word "smoke" to include alpha and beta particles, gamma rays, etc. ←Baseball Bugs What's up, Doc? carrots→ 22:46, 3 February 2015 (UTC)
 * While the sun produces helium through nuclear fusion, calling these alpha particles is a bit sketchy (technically correct, but a bit odd to do so). Alpha particles are generally what helium atoms are called when they arise from fission rather than fusion processes, specifically alpha decay.  Indisputably, a helium atom is indistinguishable from any other helium atom regardless of the process that makes it, but to call a fusion-produced helium atom an "alpha particles" feels weird.  -- Jayron 32 00:45, 4 February 2015 (UTC)


 * Solar_spectrum_en.svg you are asking what we know about the colors of light that the sun makes, see sunlight. This figure shows the amount of power at each wavelength or spectral color, both with and without the effects of our atmosphere. SemanticMantis (talk) 21:41, 3 February 2015 (UTC)


 * ♫ Caaaannnn you paint with all the colors of the wiiiinnnd... ♫ --71.104.75.148 (talk) 23:04, 3 February 2015 (UTC)


 * So, it doesn't produce smoke like, what comes out when we burn something? And gamma ray and other things that are related to long distant measurement, is the other way to define a smoke from the Sun...? Btw, I'm talking about all the colourful stars i.e., when they are in different phases... -- (Russell.mo (talk) 14:55, 4 February 2015 (UTC))
 * Different stars will have different spectra. So e.g. a red dwarf has a different color than our sun. So if you pick a certain star, say Sirius, you can often find out the spectrum of that star with some searching. Our article doesn't have a complete description of Sirius' spectrum, but it is mentioned with several references, and an analogous diagram to the one above could be made with existing data. Now, none of the stars "burn" - they do not combust, and they do not produce anything like what we call smoke (Bugs is making sort of a joke analogy above - those particles are not smoke). They produce heat and light through a totally different process, called nuclear fusion, linked above. SemanticMantis (talk) 15:08, 4 February 2015 (UTC)
 * I have read the articles stated. Not that I remember any of it, I do get the idea behind how it comes to existence, burns... I thought, since it is like fire (blue, mostly yellow reddish colour, never seen white) it might produce smoke, since the ISM is smokey most of the time with particles... Thank you for the clarification -- (Russell.mo (talk) 15:21, 4 February 2015 (UTC))
 * As you should have read in those articles, you would have seen that it (stars) does not come into existence through burning and is not fire. Stars are not fire. --OuroborosCobra (talk) 19:18, 4 February 2015 (UTC)
 * To make smoke, it would have to emit something that condensed into small solid particles. For the sun, the solar wind blows off, but it is too hot and thin to condense into solid. For some other carbon rich red giant stars the can push off enough gas that condenses into carbon particles, very similar to smoke. Other stars can blow out heavier element rich material that condenses to silicate minerals. These particles are cosmic dust. and there are dark nebulae that are very smoke like out in space.  Eg Coalsack. Some cool stars like brown dwarfs will have clouds like smoke on them. Graeme Bartlett (talk) 21:35, 4 February 2015 (UTC)
 * Okay! I get the idea... I've read all the article you stated btw... Thanks friends. Thanks for breaking it down Graeme I was actually expecting a real smoke. -- (Russell.mo (talk) 21:51, 4 February 2015 (UTC))

Gas lost from atmosphere
A topic that has come up in a science lesson but which a precise answer was unavailable is in regards to the amount of gas that is lost from the Earth each day. (Although there are also gains from volcano eruptions etc..) Assuming that there is a small amount that can drift off, how much gas from the Earth's atmosphere is in fact lost?  Dark Toon  Link  23:19, 3 February 2015 (UTC)
 * Apparently three kilograms (3 kg) of hydrogen and 50 grams (50 g) of helium per second. Atmospheric_escape --Tagishsimon (talk) 23:53, 3 February 2015 (UTC)
 * Very helpful, thank you very much. I wasn't sure what the actual term was, but now that I've read it it's quite an interesting article. Thanks again!  Dark Toon  Link  00:06, 4 February 2015 (UTC)