After reading your post about vinegar and bicarbonate of soda as cleaners, I've been using bicarb more to clean and deodorize things (a bicarb and water paste is pretty good for spills on fabrics and carpets - just massage it in then leave it overnight and vacuum it up the next day. Clogs the vacuum filter something fierce, though).
In the course of my experiments, I've found that if you add bicarb to near-boiling water, it fizzes. This is with plain water fresh out of the electric kettle, not water plus vinegar or anything else acidic. Add bicarb to the water, it fizzes and dissolves. Add more bicarb, more fizz. Add more hot WATER to the existing bicarb-and-water solution, and it fizzes again!
What's going on, here? I know dissolving stuff in water can change the boiling point, but I think it usually INCREASES it, and the difference isn't usually very large. Is the bicarb providing nucleation sites for boiling? Why's it still happen when the bicarb's dissolved, though? And how can it boil water that's not hot enough to boil naturally any more?
Suze
The Wikipedia article actually explains this; above 70 °C, sodium bicarbonate and various other bicarbonates decompose. In sodium bicarbonate's case, it goes from NaHCO3 to sodium carbonate (Na2CO3), water and carbon dioxide. The hotter it is, the faster this happens, and it happens in solution too.
So the fizz is still carbon dioxide bubbles, just as if you'd added bicarb to vinegar, but the source of the CO2 bubbles is different.
In one of Alastair Reynolds' books, someone sets off a "pinhead-sized" antimatter bomb, and it explodes with a yield of about two kilotons of TNT. Is that accurate? Would you really only need that much?
Jamila
I think you're talking about Revelation Space, the first book in that series, written slightly before Futurama debuted and so forgivable for its inclusion of a captain named Brannigan.
First, note that in a matter-antimatter explosion, you're not just converting the mass of the antimatter into energy. You're also converting an equal mass of matter, because if that matter was not around there'd be no annihilation and no explosion.
The energy yield of matter annihilation is a simple case of mass-energy equivalence, and thus subject to the famous e equals mc squared. Which is to say, energy in joules equals the mass being annihilated in kilograms times the square of the speed of light in metres per second.
The dominant number there is obviously c-squared; the speed of light in vacuum is 299,792,458m/s, and squaring that gives you 89,875,517,873,681,800. Or, in less-cumbersome scientific notation about 8.99E+16 - 8.99 times ten to the power of 16.
"TNT equivalent" bomb-yield numbers are tightly defined, too; one ton of TNT is defined as 4.184 gigajoules.
Now, what's a pinhead weigh?
I just grabbed some ordinary one-inch dressmakers' pins and found there were about fifteen whole pins to the gram. I'm not about to snip off enough pinheads to get them to add up to the minimum resolution of my triple-beam balance, but I'd guess the mass of these pins' heads to be ten milligrams, at most.
Fortunately, the mass of the Revelation Space bomb is mentioned in the book; it's described as containing "only a twentieth of a gramme of antilithium". That's fifty milligrams, but that doesn't sound like a crazy weight for the head of a stouter pin than the ones I weighed.
Plugging fifty milligrams, 0.00005 kilograms, into e=mc^2 gives
e = 0.00005 * c^2
= 4.49378E+12 joules
= 4494 gigajoules
...which at 4.184 gigajoules per ton of TNT, adds up to 1.074 kilotons. Double that to take into account the matter that's annihilating with the antimatter, and you get 2.148 kilotons. Which is indeed close enough to two kilotons for horseshoes, hand grenades and tactical nuclear weapons.
The biggest thermonuclear explosion ever created by humans, the immense and impractical Soviet "Tsar Bomba", had a possible yield of about 100 megatons, but was dialled down to 50. 50 megatons at 4.184 gigajoules per ton is 2.092E+17 joules. Turning e=mc^2 around to solve for mass, m = e/c^2, gives:
m = 2.092E+17 / c^2
= 2.33 kilograms of matter converted into energy, for the biggest bomb we've ever made, and possibly the biggest bomb we ever will make.
Around the weight of a healthy adult chihuahua.
(See also solid blocks of electrons, which knock antimatter energy density into a cocked hat and which may be a technology within the reach of some entities in the Revelation Space universe. Oh, and see also, also, the fun you could have whacking lumps of plutonium together by hand.)
why do some things glow brightly in colours OTHER THAN BLUE when illuminated by a blue LED flashlight? Is it fluorescence? But doesn't that only happen under ultraviolet light?
Does this mean my blue LED flashlight has UV output? it's incredibly bright, but is it actually even brighter and more dangerous than it looks?
Ant
First up: I highly recommend coloured LED flashlights. They let you do this!
The above animation accurately reproduces what it was like for me selecting the images to use to illustrate this post, except I was doing it fullscreen on a 30-inch monitor, and so almost neutralised my neurons.
(If you're using Chrome and are now hammering away on the escape key in a desperate attempt to make this brain-slapping animation stop, allow me to suggest the GIF Stopper extension.)
In the olden days, the only coloured portable lights normal humans could afford used an incandescent bulb, with a coloured filter over it. This was incredibly inefficient, and usually didn't even give you one tightly-defined wavelength of light. Your green-filtered flashlight probably still emitted some red and blue.
Today, you can get high-intensity coloured LEDs with a very tight band of output frequencies; no blue in your green, no green in your red. I think the best-value options are the coloured variants of the Ultrafire 501B lights.
I reviewed a white 501B years ago here, but this line of lights still sells well today, because they're basically just SureFire knockoffs with standardised lamps and battery compartments. So you can today buy a white 501B that's quite a bit brighter than the one I reviewed, or upgrade your old 501B with a newer interchangeable lamp, or stick a cheap coloured Ultrafire lamp in your old SureFire incandescent flashlight, et cetera. As long as you stick with a single 18650 lithium rechargeable or two rechargeable or non-rechargeable 123-size cells. Any cheap LED module that's meant to fit in a a flashlight like this should work.
(As Fallingwater points out in the comments, there are also lamps this same shape that want a very different input voltage, and the dirt-cheap lamps may not work very well for various reasons. I think all of the cheap coloured lamps are for one or two lithium cells, though, and they're low-powered by "tactical flashlight" standards so don't have heat problems either. These lamps work from one or two cells because they have a multi-voltage driver. Incandescent bulbs are not this tolerant. Standard small two-123-cell SureFire-type lights with incandescent bulbs will produce a dim orange light from a single 18650. If you somehow manage to drive an incandescent bulb from twice as many cells as it expects, it will die immediately.)
Here's an eBay search that finds a bunch of coloured Ultrafire flashlights and lamps. The lamps start at $US9.99 delivered, but a whole flashlight (without batteries) is under $US15 delivered.
A red, a green and a blue Ultrafire 501B, plus three 18650s and a charger from eBay will only cost you about $US50 all told. The cheapest dealers all have free shipping, too, so you can buy the lights one at a time and not lose any money.
I'd really get all of them, though, and I don't even go to raves. It's just so much fun chucking large amounts of coloured light around. And yes, you do get a pretty decent white-ish light if you shine them all at the same thing.
(See also the positively antiquated Technology Associates "Rave'n 2", which I reviewed more than ten years ago and which I think they still sell. It's still fun, too.)
So. Where was I? Oh yes, fluorescence.
Fluorescence happens when a substance absorbs some kind of radiation, usually light, and then emits light of its own.
It happens when the incoming energy, usually a photon, "excites" an electron to a higher quantum state. When the electron then "relaxes" back to its ground state, it loses some energy to heat and emits the rest as a new photon.
Since the energy and frequency of a photon are directly related, and the outgoing photon is less energetic than the incoming one was, one-photon fluorescence like this only works "downward" in the ROYGBIV spectrum. You'll only see visible-light fluorescence when you're illuminating a fluorescent object with light closer to the blue end of the spectrum than the colour the object fluoresces.
("Upwards" fluorescence is actually possible, when two photons are absorbed but only one emitted. I think this is pretty much unknown in everyday, visible-light fluorescence, though.)
Ultraviolet light is beyond the blue end of the visible spectrum, so it can cause fluorescence in any visible colour. But there's no rule that says the incoming light can't be visible; it just has to be further up the spectrum than the colour of fluorescence it creates.
So here are some brightly-coloured objects from around my house, illuminated by tungsten-filament bulbs. Some of the dyes used to colour many modern polymers are highly fluorescent; shining an ultraviolet light around your house is the best way to find them, but a blue LED flashlight will do a good job too.
A red flashlight's no use, though. It's probably possible for red light to cause visible fluorescence that's even deeper into the red, but you'd probably need a spectrometer to distinguish it from simple reflection of the illuminating light.
Here, we see what basic colour theory says we should. All we're seeing is the red light that bounces off the scene, so everything is shades of red, and the less red there is in the colour of an object, the less of the incoming light will bounce off it and the closer to black it will look.
Go to green light, though - not even blue! - and suddenly fluorescence is happening. The red Gakken mini theremin (as hard to play as a full-sized theremin, but with the mellow, soothing tone of a Stylophone! Buy one today!), and the red rubber Escher's solid (sold as a dog chew toy, of all things, at my local discount shop), and the red crooked dice, are behaving as basic colour theory says they should. There's no green in them, so they look black.
The orange parts of the Nerf guns, though, are cheerfully fluorescing under the bright green light.
(Actually, only the little "Secret Strike" is a Nerf product; the double-barrelled gun is a Buzz Bee Double Shot, which ejects the empty shells when you break it open!)
I think the yellow parts of the toy guns may be fluorescing a bit under green as well. They mainly look yellow only in comparison with the fluorescing orange plastic (as per this amazing optical illusion), and my digital camera certainly isn't a calibrated colourimeter, but there's still a significant amount of red in there with the bouncing green. That adds up to at least a yellow-ish green.
The length of red paracord (useful for all sorts of things, and also the only flexible string I've found that Joey's little razor teeth don't go straight through) and the carapace of the crab Hexbug, aren't as fluorescent as the plastic, but they're having a go.
Oh, and check out the two HobermanSwitch Pitch balls. One is green and orange and is fluorescing a little and reflecting rather more in the green light; the other is blue and magenta, and is hardly fluorescing at all.
(The Switch Pitch is, I think, one of the greatest fiddle-toys ever invented. I know this post's littered with affiliate links, but seriously, buy a Switch Pitch, if you can. Not everything Hoberman make is a classic; the Brain Twist, for instance, is a worthy attempt at Hoberman-ifying a Rubik's Cube, but I reckon it's more of an ornament than a toy. But the Switch Pitch and the tougher, hard-to-find Switch Kick, are brilliant.)
OK, on to the blue light that started this interminable thing.
Now the lower-fluorescers from the green-lit shot are fluorescing with more enthusiasm, the things that never fluoresced in the green are still sticking to pre-quantum-physics colour theory, and the orange plastic has gone nuts. There's a pretty sizeable energy gap between LED-blue and that orange, so it's sucking up and spitting out electrons photons with great enthusiasm.
My own store of quantum energy ran out before I made an actual UV-lit version of the picture, but I could pretty much just Photoshop one up in less time. All of the fluorescing things in the blue-lit image would look much the same under UV, and everything else would be invisible. Or, more realistically, you'd see everything else in faint blue, because the ultraviolet compact-fluorescent lamps I've got here emit a fair bit of visible blue-violet light along with the UV.
You can get UV LEDs that emit proper near-UV light (not the more dangerous UV-B or even more dangerous "germicidal" UV-C) with very little visible output. Most "UV" LED flashlights use cheaper purple LEDs, though, which may have a bit of near-UV output but basically just do what a blue LED light does, only more so.
And yes, you can get UV Ultrafires, too, but I don't know which flavour of "UV" LED they contain.
How come NASA spacecraft need all that heat shielding, but SpaceShipOne and Two don't? Does this have something to do with escape velocity - they don't go that fast, so they fall back down when the engines stop and don't have to re-enter. But they do get outside the atmosphere, right? Is there more than one kind of re-entry?
Cherie
There's no clear line where "the atmosphere" stops. By convention, the Kármán line at an altitude of 100 kilometres is treated as the end of the atmosphere; SpaceShipOne made it to 112 kilometres, and SpaceShipTwo is intended to do the same, but with more people on board. But satellites in low orbit well above the hundred-kilometre line need periodic re-boosting to compensate for the drag of the tenuous outer reaches of the atmosphere. Take the International Space Station, for instance; it orbits from 330 to 410 kilometres up, but still needs periodic re-boosting to prevent its orbit decaying. This goes for anything else delivered or serviced by the Space Shuttle, too; inability to reach high orbit was one of the Shuttle's numerous shortcomings.
(The Shuttle carried some satellites that ended up in high orbits, and even space probes that left earth behind entirely, but those payloads needed their own booster rockets for the second part of the trip.)
(Oh, and orbital decay also shows up in umpteen Star Trek episodes as another Acme Mechanically-Assisted Plot-Tensioner, even when the Enterprise seems to be orbiting way above the conceivable atmosphere of any earth-like planet. Presumably they deliberately keep themselves in a super-slow pseudo-orbit by use of engine power, because... tech tech tech.)
You could say that "re-entry" means any trip from orbital altitude back into the atmosphere, but what most people mean when they use the term is a trip from an actual orbit back into the atmosphere. That's where the big difference lies, because orbital velocity is high.
Low-orbital velocity is particularly high, because the closer an orbiting object is to the thing that it's orbiting, the stronger will be the gravitational pull on it, and the higher its orbital speed must be, for it to actually be in orbit and not just fall back down.
The earth, orbiting approximately 150 million kilometres from the (very large mass of the) sun, takes a year to go around it once, travelling at about thirty kilometres per second.
The moon orbits approximately 385,000 kilometres from the earth; if the earth had the mass of the sun then the moon's orbit would be extremely fast at that relatively small distance - Mercury, orbits the sun at an average distance of about 58 million kilometres, and travels at about 48 kilometres per second. But because the earth is much less massive than the sun, the moon takes 27.3 days to go around us once, travelling at only about one kilometre per second relative to us.
The International Space Station's low orbit takes it around the planet in only about ninety minutes; it therefore travels at about 7.7 kilometres per second, more than 22 times the speed of sound at sea level.
Re-entry is still a problem even if you're out in a very distant and slow orbit, though, because you can't just teleport from that distant orbit to the edge of the atmosphere. You have to use something - rockets, or some gravity-assist trick around some other body - to reduce your orbital velocity, putting you on a new orbit that intersects the planet's atmosphere, preferably in a survivable way.
That orbital adjustment reduces your speed relative to the planet, but then your new elliptical path means you fall toward the planet at greater and greater speed. Five hours before splashdown at the end of the Apollo 11 mission, the spacecraft was about 76,000 kilometres from the earth and approaching the planet at less than three kilometres per second. Five and a half hours later, as the spacecraft started to catch some real atmosphere and lose radio contact, they were still about 3,000 kilometres from their splashdown point (including a large diagonal component, since they weren't plunging straight down toward the planet), and were now moving at eleven kilometres per second.
(There's a lot more complexity to orbits and de-orbiting in the real world, of course, not least because many orbits are far from circular, with a slow portion further from the planet and a fast portion closer to it. Such orbits can be ratheruseful, and various advanced and less-advanced simulators exist to help you get a feel for them.)
So one way or another, a return to the earth from orbit or from a trip to some other part of the solar system involves very high speeds. Such high speeds, in fact, that friction with the air contributes little to the heating effect; it's air piling up in front of you and trying to get out of your way, and being heated by hypersonic compression, that creates the glowing plasma halo and glowing-hot heat shields on re-entering spacecraft.
You can avoid all of this if, like SpaceShipOne and Two and other "sub-orbital" vessels, you never get anywhere near orbital velocity, and just fly up until the sky is black and the earth is curved, then fall back down. When you start to fall there's little air resistance and almost as much gravity as at the surface of the earth (even the International Space Station is close enough to the earth that it's subject to gravity about nine-tenths as strong as at sea level), so you can get up to some moderately impressive speeds by aeroplane standards. But you're a long way from true re-entry speed.
For comparison, the fastest aircraft humans have ever managed to make that truly qualifies as an aircraft - takes off and lands under its own power, can be refuelled and re-used, has enough fuel to fly a reasonable distance, carries living humans and usually keeps them that way - is the Lockheed SR-71 spy plane. Most of the SR-71's technology remains impressive today and was nearly miraculous in 1964, but the thing was such a nuisance to operate (and was largely superseded by satellites and drones) that it's now been retired in favour of its 1950s predecessor, the glider-like U-2, maximum speed only impressive by World War II standards.
Flat out, with its skin hot enough to melt lead and five kilograms of fuel going into the engines per second, the SR-71 could manage about one kilometre per second.
That's nine times the speed of the fastest production car, three times the land speed record, and quite close to the muzzle velocity of the most outrageously fast rifle bullets. But any random piece of dead-satellite or rocket-casing space junk that fireballs its way to destruction in the atmosphere is pretty much certain to beat the SR-71 by a factor of at least ten. Space Shuttle re-entry was carefully controlled to get it under nine kilometres per second before it started really heating up, but you can see why it was such a big deal when Columbia had a hole the size of a saucer in one leading edge.
You can avoid all this, too, if you've got a lot more engine power to play with. Come up with a sci-fi drive that can deliver lots of thrust for long periods of time with little vehicle mass (in technical terms, both large thrust and very high specific impulse; the closest we've managed to come to these goals has been strangely unpopular...), and you can leave the atmosphere as slowly as you like, accelerate to orbital velocity as slowly as you like, and generally Superman your way around the solar system without having to endlessly account for every joule and newton lest you end up drifting to Neptune while your air runs out, or turn into an array of orange streaks across the sky.
This is where "escape velocity" comes in, too. Escape velocity (more correctly, in physics terms, escape speed, since direction is irrelevant) is how fast you need to be going, from wherever you currently are, to break free of the gravity of a given body. If you're at sea level on an earth with a magic spaceship that is not subject to air resistance, then 11.2 kilometres per second is the speed you need. If you shoot off in any direction (even, theoretically, through the planet, if your magic spaceship is also not subject to ground resistance...) at 11.2 kilometres per second, you're not going to come back down.
Escape velocity on the moon (where air resistance really isn't a problem) is only 2.4 kilometres per second, but Alan Shepard's golf balls definitely did come back down. They probably wouldn't have on Phobos or Deimos, though, because those tiny bodies' escape velocities are only 11.3 and 5.6 metres per second, respectively.
Escape velocity isn't of much direct relevance to Earth-launched spacecraft, though, because something shot out of an 11.2-kilometre-per-second cannon at sea level will definitely come back down after atmospheric drag eats most of that speed. The great problem of getting things up out of our atmosphere and gravity well when all you have to propel them are poxy chemical rockets is finding a way to strike a balance between having lots of rocket power, and using most of that power just to launch the fuel and engines that you need to launch the fuel and engines that you need to launch... You get the idea.
How the hell did "prune juice" ever come to exist, since a prune is a dried plum and you can't get juice out of dried fruit? Do they mash them up and add water or something?
Isaac
There's a loophole.
Plums grown primarily to be dried are called "prunes", even before they're dried. They can also be eaten fresh, or juiced. Presto, a warrior's drink.
And now, some Bonus Botanical Trivia:
Many people believe nectarines to be a peach/plum hybrid. They're not. They're a smooth-skinned strain of peach, sharing an ancestor with the plum somewhere back in the history of stonefruit, but otherwise unrelated.
Somewhat fewer people believe nashi pears to be an apple/pear hybrid. They're not. They're a natural species, or, at any rate, as "natural" as the apples and pears that humans have been selectively breeding for thousands of years.
(I am greatly amused by Creationist publications that show a magnificent spread of delicious fruit and veg that God in His wisdom has provided for us; the Jehovah's Witnesses have a really nice version of this in one of their numerous happy-pictured books and pamphlets. I always have a hard time finding anything in those pictures that hasn't been gigantically changed from a near-inedible ancestor by human intervention. Possibly the coconut. Good luck opening that with your bare hands, Adam.)
Lemons, on the other hand, are a hybrid, though a pretty ancient one. Genetic analysis (PDF) has shown them to be a hybrid of the bitter orange and the citron.
If you always thought that grapefruit were hybrids too, you'll now be amazed to learn that you were right. The grapefruit only dates back to the 18th century.
Many people are also familiar with the factoid that, technically, the banana is a herb. Banana taxonomy has always been a nuisance, but this bit of pub-trivia information is not actually worth much.
In everyday grocery-shopping terms the banana is obviously a fruit, but in botanical terms it can defensibly be described as a berry, while the botanical "herb" is any non-woody flowering plant, most of which are inedible. (And, by the botanical definition, each individual kernel on an ear of corn is a separate "fruit". Don't get me started on cashews.)
All of these games with definitions and clashes between scientific and everyday terminology are pretty pointless. They make about as much sense as saying that because people who make coins for a living may refer to all of their input metals as "bullion", it is therefore sensible to invest in copper by the ounce.
Another one: In everyday usage, hardwood means wood that is hard. In scientific terms, though, it just means wood from non-flowering flowering [it wasinevitable I'd get one of these wrong, wasn't it?] plants, so balsa wood is technically a hardwood.
Finally, and perhaps most interestingly, it turns out that the tomato is technically an amphibian.
My mom's always been a strong proponent of vinegar as a miracle cleaner for almost anything, floors, windows, clothes, you name it. She recently discovered bicarbonate of soda, too, and has been using that for all sorts of stuff too, like in the dishwasher instead of the special powder.
When I visited the other day, she was washing the floors with a bucket that had hot water, bicarbonate of soda AND vinegar in it. Apparently the fizz when you add the vinegar gives you more "scrubbing bubbles". Except I vaguely remember from elementary school that an acid and a base cancel each other out, the example given having been exactly this, vinegar and washing soda.
So was my mom just washing the floor with salty water?
Bicarb is NaHCO3, acetic acid is CH3CO2H. Acetic is the acid in vinegar - cheap "white vinegar", which is rather more economical for cleaning things than 50-year-old balsamic, contains nothing but nice clean industrial acetic acid and water.
The reaction is:
NaHCO3 + CH3CO2H -> CH3COONa + H2O + CO2
Those products are sodium acetate, water and carbon dioxide. The CO2 is invisible but heavier than air, and can be poured out of the reaction container to extinguish a candle, said candle being the most dangerous thing that exists in boringly-safe-science demonstrations.
Sodium acetate is sometimes used as a flavouring, because it tastes like salt and vinegar all by itself. ("Salt and vinegar" snacks in the USA are apparently likely to be flavoured with sodium acetate; here in Australia I think that's illegal for some reason. I don't think it's toxicity; sodium acetate is pretty innocuous.)
If you mix sodium bicarbonate and hydrochloric acid, HCl, then the reaction is the same except instead of sodium acetate, you get sodium chloride, which is everyday table salt.
(For this reason, bicarb is a very effective antacid. A teaspoon full of bicarb can turn nasty acid-reflux indigestion into a series of hugely satisfying CO2 belches in seconds. You'll have a pretty darn high-sodium diet, though, if like me you end up eating several spoonfulls of the not-that-bad-tasting-when-you-get-used-to-it substance per day. In that case, hie thee to a doctor and get yourself a prescription for one or another acid-production-reducing drug.)
You'd want to be careful making salt from bicarb and hydrochloric acid, though, because if you don't get your stoichiometry right and not add balanced amounts of the reagents, then there'll be left-over bicarb or hydrochloric acid at the end. This is also what will happen if someone decides to make a cleaning product out of bicarb and vinegar; they probably won't titrate the mixture, and so will have a surplus of one substance or the other. Surplus bicarb, as a base, will clean greasy things by, essentially, turning the grease into soap. Surplus vinegar, as an acid, will clean things by dissolving various kinds of dirt, like mineral deposits ("scale"), or rust.
For these reasons, and also the fact that plain water plus elbow grease can clean a lot of things pretty effectively (the basis for the popularity of "laundry balls", which don't actually do anything), people may come to the conclusion that a vinegar-and-bicarb concoction is a super cleaner, when in fact they'd be better off using a smaller amount of only one of the ingredients.
(At least, in this case, mixing the compounds will do no harm. Mixing bleach and ammonia, on the other hand, may greatly reduce the amount of time you spend doing household chores, on account of how you may now be dead.)
Oh, and sodium bicarbonate is not "washing soda"; that's sodium carbonate, Na2CO3, which is commonly used to "soften" hard water, which contains dissolved minerals that prevent soap from working properly. Sodium bicarbonate is "baking soda", named for its use as a leavening agent; if you mix bicarb into batter that's slightly acidic, the fizzy-neutralisation reaction occurs and creates lots of little CO2 bubbles in the batter. "Baking powder" contains dry bicarb and acid powder (usually tartaric acid). Add water, and the components react and fizz.
Getting back to sodium acetate, a supersaturated solution of it is used in "phase change" heat packs...
...which "freeze", liberating heat, when disturbed with the little clicker device inside, or when otherwise slapped around. You put the pouch in boiling water to re-liquefy its contents; the things can be used over and over indefinitely, as long as they don't spring a leak.
You can do something similar to this with numerous other fluids, but sodium acetate's properties suit it very well to the purpose. Even if you don't actually need a hand-warmer, I strongly recommend you buy one as a toy, since you can get them on eBay for about $5 delivered.
All I really know about it is that it's technically called "cyanoacrylate", but the "cyano" part makes me nervous. The last episode of Mythbusters I saw had them sticking stuff to other stuff with superglue (which they called "super adhesive" for some reason) and they were wearing gas masks while doing it.
Am I endangering my health if I superglue a teacup together without lots of ventilation? My son's just now started building model airplanes and tends to stare so close at the model I'm expecting him to stick a propellor to his nose soon; is HE going to be poisoned too?!
Eva
At some point in the next few thousand words I may answer your question, Eva. You know how it is with me.
The magic acronym (or possibly initialism) to remember whenever you want to know how strongly a given substance desires to kill you is "MSDS", for Material Safety Data Sheet. You can find an MSDS for just about anything, provided you know the name of the substance in question. You usually don't need to know the exact chemical name, either; brand names, especially of pharmaceuticals, often work.
One popular substance can have a large number of MSDSes for it, sometimes with different data, because, for instance, a product sold under the same name by different companies may be made with different constituents. MSDSes may also differ even when they're talking about the exact same substance, because different manufacturers and importers and so on may have different testing regimes, or may just plain get stuff wrong. Generally speaking, though, you can trust MSDSes, even if you can't find one for the exact brand of, in this case, cyanoacrylate (which is known to the relevant chemists, and many hobbyists, as "CA") you're worried about.
When I say "just about anything" above, I mean it. Here's an MSDS (in PDF format, like most online MSDSes these days), for skim milk. Including rather excessive first aid procedures to employ in case the substance is ingested.
Here's one, and another, for olive oil. More over-enthusiastic warnings; apparently you're not meant to allow olive oil to make direct contact with the skin. MSDSes for innocuous substances are often like this, possibly for reasons having to do with the covering of arses, or perhaps because there was no "zero hazard" box for the MSDS-maker to tick.
OK, enough silliness. Search for MSDSes for cyanoacrylate, plus a common brand name or two like "Krazy Glue", and you'll get hits like this, this, this and this. Here's a whole page of MSDSes for Loctite products, including various other glues and threadlocks. There's a "safety" section in the Wikipedia article for CA, too, plus some MSDS links at the end.
What all of these agree on is that CA products of various kinds, from the water-thin stuff used to wick into gaps in plastic models through to various non-runny gel-type versions, are not nearly as poisonous as you'd think from their alarming "chemical" odour. The fumes are an eye and mucous-membrane irritant, and if you're sticking a whole room worth of furniture to the ceiling as they did on MythBusters then you'd be nuts not to wear some kind of breathing protection, but this stuff really isn't that bad. I don't think it even releases much in the way of horrifyingly deadly gases if you burn it, though again, this is not recommended.
(With regard to the title of this post, glues that people sniff to get high in a rather dangerous manner are generally based on some kind of solvent with psychoactive effects, though usually not effects that people living a life somewhere above rock bottom would consider worth the damage. Glues with no such solvent, like CA, PVA, hide glue or epoxy, often aren't particularly bad to inhale, which is just as well since they won't even get you high.)
Part of the reason why superglue isn't very poisonous is that its "set" state, a hard polymerised lump, isn't toxic. It's still listed as an "eye irritant" when hardened, but only in the way that sand is. And CA really wants to polymerise. All actual CA glue contains "inhibitor" chemicals in addition to the CA itself, to stop the stuff from instantly turning into a lump of plastic in the bottle. Several common compounds in the world, chief among them water, will "kick" CA into polymerising. And since your eyes and mucous membranes and so on are all rather damp, any CA vapour that hits them polymerises instantly.
Now, this is still not a good situation, since having a very thin layer of plastic accumulate inside your nose and on your eyeballs is not most people's idea of a good time, but the body can deal with tiny amounts of the stuff with no trouble. (This also means that all you probably need as the abovementioned "breathing protection" is a damp cloth tied around your face.)
You can take advantage of the effect water has on CA to accelerate its bonding, by for instance breathing heavily on the two pieces of something you're gluing before bringing them together, or even by spitting on the glue, in extremis. That won't give you a very good bond, but if you're in a hurry, it'll do. You can also sprinkle bicarbonate of soda on the glue, or dribble CA onto bicarb, to get an instantly set, hard but brittle filler material. (It's basically Bondo for plastic spaceships.)
There are also liquids, known as "CA accelerators" or "kickers", that give you an almost instant full-strength bond when they touch CA. You generally put glue on one piece, a spritz of accelerator on the other, then bring them together and zap, instant gluing of two parts that you didn't quite bring together straight, god damn it.
I'm not sure how much variation there is between the different accelerators; these days I just buy whatever's cheapest on eBay. Note that CA accelerator tends to be rather volatile and thus prone to liberate itself from the spray-bottle faster than many people can use the stuff. I recommend you keep the sprayer in a Ziploc bag.
The fact that there are substances that kick CA better than water does is the base for products like the one described in this MSDS, which is for a CA formulation used for fingerprint "fuming". You can do this neat little science trick with any CA, not just special expensive law-enforcement CA:
One thing hobbyists discover pretty quickly about CA, especially if they're using accelerator as well, is that the polymerisation process is exothermic. The glue gets warm as it polymerises, the increased temperature speeds up the polymerisation, and with enough glue and enough accelerator (or just CA by itself, if it's on something with a lot of surface area - cotton is particularly bad) the result is boiling polymerising CA. I don't trust any hobbyist who hasn't emptied five whole dollars worth of discount-store superglue into a very disposable container in the back garden, then added some generous squirts of accelerator, and stood well back.
This is another CA hazard. If you spill a lot of it on your cotton-denim jeans (or somehow just manage to deliberately use an unusually large amount), the profoundly crappy time you'd reasonably expect to have in your immediate future may be made significantly crappier by some nasty burns.
Anybody who's ever used superglue will have stuck the wrong things together, though with any luck just one finger to another, not a square foot of garment to singed flesh. If possible, a good way to remove CA is mechanically, with sandpaper or a file or, for many glue-on-skin situations, a disposable razor. (Or you can just wait; as the outer layer of your skin naturally flakes off, the glue will go with it.)
CA can also be dissolved with acetone, but the MSDSes for acetone are rathermorealarming than those for CA. There are less toxic glue debonders out there too; again, please accept my very personal recommendation of whatever's cheapest on eBay and isn't just acetone.
(CA is also not just kicked into polymerisation by water, but also slightly soluble in it. So a long hot bath or shower may help you out, provided you have enough un-stuck limbs to be able to operate the taps.)
While I'm giving unrequested buying advice, as far as CA itself goes, I just buy it from discount shops. Given CA's irritating propensity to go hard in the bottle, I like the few-dollar cardboard oblongs with multiple little separately-bubble-packed tubes, the more and the smaller the better. Unless you've got an ongoing meaningful relationship with a local hobby shop - which I recommend; it's worth paying a bit extra for stuff if wise counsel on various subjects, or just hours of entertaining chat, is available in return - I see no reason to buy fancy brand-name CA for almost any job.
Getting back to that alarming cyano group which is indeed hanging off the few different, but effectively almost identical, kinds of CA molecule, it is in this case not much to worry about, but certainly is if it's hanging off something less complex, like a potassium or hydrogen atom. I find the lethality of various cyanide compounds almost amusing, since it's yet another sign of the absence of "intelligent design" of even this one planet, let alone the whole universe.
I mean, what's the element that's the basis of all life on this planet? Carbon. What makes up 78% of the planet's atmosphere? Nitrogen. (Don't miss this sample!) What do you get when the two of them get together? Cyanide, a deadly poison. It's sort of the opposite of the sodium-plus-chlorine thing.
And while I'm rabbiting on, I was also amused by MythBusters' and/or Discovery Channel's determination to call the glue they were using "super adhesive", a term that doesn't really exist in nature, to the point where a couple of slip-ups when someone said "superglue" anyway made it to air. This is in line with MythBusters' general self-censorship policy, in which no brands not integral to the myth are blurred or taped over or covered with new labels reminiscent of Repo Man.
Sometimes this policy seems to make little sense, though. In a recent special episode, MythBusters shot a .50 AE round from a Desert Eagle into watermelons, and they called the gun a Desert Eagle, even though there are various other firearms that chamber that round. But in the episode a while back where they demonstrated what a bad idea it is to wrap your hand around the cylinder of a .50 Smith & Wesson revolver when firing it, not one mention was there of the brand of that gun, though anybody familiar with the preposterous hand-cannon arms race of recent years could have mistaken a S&W Model 500 for anything else.
(If you haven't been watching the nutty progression of ever-more-wrist-smashingly-powerful handgun cartridges and the you've-gotta-be-kidding-me guns that shoot them, compared to which the action-movie-staple .50 AE Desert Eagle's .44-Magnum-ish bullet energy looks positively feeble, then you could be forgiven for thinking a short-barreled Model 500 was some kind of flare gun. I wonder if even this has been surpassed by now?)
The "super adhesive" thing is particularly nutty, though, since they could have just called it cyanoacrylate.
Why do nuclear power stations (and other power stations, for that matter) have cooling towers in that weird half-hourglass shape?
I presume the guys who built them knew what they were doing, but what did they know that I don't?
Ian
I pledge to eventually answer your question, Ian, but first I'm going to rabbit on interminably about power stations.
The cooling tower has become emblematic of nuclear power stations, and the white "smoke" drifting from the top of them is a source of vague nervousness for a lot of people.
But, as you say, other kinds of power stations have cooling towers too. I live less than an hour's drive from Lithgow and the Mount Piper and Wallerawang Power Stations, able to produce 3.4 gigawatts of coal-fired electricity between them; Mount Piper has two cooling towers, Wallerawang has one. The "smoke" that comes out of these towers is actually just clouds of tiny water droplets.
(Once again, if you can see it, it's not "water vapour". Clouds, and the visible "steam" squirting out of a kettle or a steam locomotive, are liquid water droplets with a ceiling temperature of 100°C at sea-level air pressure. It's possible for actual invisible-vapour steam to be swirled in with condensed droplets as it mixes more or less chaotically with the outside air, but "pure" steam is invisible, and has no ceiling temperature. Put your hand in the visible portion of the steam coming out of the side of a locomotive and you may get scalded, but putting your hand in the invisible jet close to where it's exiting may flense the flesh from your bones.)
Power stations need cooling towers, or some other heat-sink like water from a convenient river, because they are heat engines. Heat engines, as I've written before, become more and more effective as the temperature difference between their "hot end" and their "cold end" increases.
A heat-engine that makes this fact obvious is the now-quite-standardised sort of "coffee cup" Stirling engine...
...which stands on a wide circular displacer-piston cylinder and can run on the heat from a cup of coffee or tea, or backwards on a cup of ice-water. I've got one that runs like this, but really low-friction versions of the design can run on the heat from a human hand, if the ambient temperature is cool.
(You can pay quite a lot of money for a jewel-like Stirling engine {or, more interestingly, a kit to build one}, but this eBay dealer, in addition to being called "Stirlingeezer" which ought to be a reason to buy from him all by itself, sells quite beautiful engines and kits that are guaranteed to run from hand-heat. If enough people buy stuff via the above affiliate link to Stirlingeezer, I shall soon be able to afford one of his engines!)
(Oh, and if you're short of money, you can get a Stirling kit for $US30 delivered, or conceivably less if you get lucky with your bids, from this guy in China.)
Conventional power stations, whether fired by coal, combustible gas of one kind or another, or a nuclear reactor, make their electricity by turning a turbine connected to a generator. Gas-fired stations can do this directly with a gas turbine, which is essentially a jet engine tuned for shaft-turning power, rather than thrust. Coal and nuclear stations make electricity less directly, by using the heat of combustion or nuclear fission to boil water and run a steam turbine.
(I think there are also gas power stations that use steam turbines. There are definitely gas power stations that burn the gas in one turbine, and then run another, different turbine from the hot exhaust of the first one.)
Anyway, that's the hot end. A well-designed heat engine will try to get its cold end as distant in temperature from the hot end as is practically possible. The ratio between the two temperatures, expressed in Kelvin (or any other temperature scale, as long as it starts at absolute zero), determines the maximum possible efficiency of a heat engine.
Sometimes "the cold end" is synonymous with "the exhaust temperature"; that's how it works for internal-combustion piston vehicle engines, and steam engines too. A classic example of the latter is the triple-expansion compound steam engine. This has one small piston for the fresh, hot, high-pressure steam right out of the boiler. The medium-heat, medium-pressure exhaust from this first piston powers a medium-sized piston, and the low-heat, low-pressure exhaust from that piston in turn runs one or more even bigger pistons. (This can theoretically be extended to even more stages, but in practice quadruple-expansion was about as far as anyone could get before the gain in efficiency wasn't worth the extra complexity and friction.)
Steam-turbine power stations, on the other hand, may emit exhaust gases from the burning of fossil fuels, but the system that makes the actual electricity is a closed, Rankine-cycle steam/water circuit. The burning fuel or fissioning atoms heat cool water to steam, the steam turns a turbine or three, and the turbine exhaust then goes to some sort of cooling device, generally a heat exchanger, that dumps the final unusable portion of the water's heat somewhere.
This "somewhere" can be a separate water supply, either a river, large lake or sea, or it can be evaporating water in a cooling tower. Once the heat exchanger has cooled the closed system's water in whichever way, that water is pumped into the boiler again, and the cycle continues.
You might wonder why you need to dump heat from the turbine exhaust, when you're only going to heat the water up again in the boiler. There are two practical reasons for this.
The first reason is that the exhaust from a power turbine is almost all still water vapour, because, in brief, turbines made to run on a flow of hot gas do not like it if the gas condenses to liquid inside them.
The second reason is that the pump that returns the water to the boiler has the opposite preference; it only works with liquid water. It would be possible to use a gas pump instead and make a system in which the working fluid is always vapour, but the energy needed to run a gas pump against pressure from the boiler is high, while the energy needed to run a water pump is trivial (by power-station standards), on account of the incompressibility of the water.
The upshot of all this is that standard 20th-century power stations are pretty miserably inefficient. Today, there's much more effort being made to reduce the heat wasted, by for instance transferring some of the heat of the turbine exhaust to the water feed between the pump and the boiler, or by using some of the waste heat to keep nearby buildings warm ("cogeneration"). These sorts of measures can only go so far, though, so cooling towers of one shape or another will continue to be built.
Which, finally, brings us back to the classic cooling-tower shape.
Cooling towers actually come in all shapes and sizes; large air conditioners, for instance, often have evaporative coolers for their chillers, but those coolers don't look anything like a power-station cooling tower.
Power-station coolers have to have very large capacity, so they inescapably have to be very large. Power-station coolers also have to provide a decent convective "stack effect", also known as "draught" (or "draft", in the less-demented American spelling). But, importantly, power-station coolers don't really need to be able to hold up much more than their own weight, plus any remotely plausible wind loads or shifts of their foundations.
The classic curvy cooling-tower shape fits all of these requirements. In engineering terms, because cooling towers don't need to hold up an interior full of offices, they can be built as a "thin-shell structure". You could build a cooling tower out of giant Great-Pyramid stone blocks if you wanted to, but a surprisingly thin reinforced-concrete shell, built in layers from bottom to top (not unlike the way 3D printers work), is the usual solution. And the builders almost never balls it up.
Objects of this shape are called "hyperboloid structures"; they're strong for their weight and so have been used for all sorts of masts and towers and, sometimes, ordinary buildings too, and they're particularly suited for use as cooling towers. The large area at the bottom of the hyperboloid gives lots of room for evaporation, the "waist" accelerates the gas mixture (I think because of the venturi effect), and then the widening opening at the top encourages turbulent mixing with the ambient air. (Air gets into the tower in the first place via an open latticework section around the base.)
The final question that occurs to me in this area is why cooling towers are hyperboloids, but factory chimneys are cylindrical (or close to it - they often taper a bit toward the top).
This is because the cooling tower wants to move a vast amount of low-pressure air. The evaporating warm water at the bottom of the tower produces a steam/air/water mixture that isn't much warmer, and thus less dense, than the ambient air, so it has little buoyancy compared with the ambient air, won't move terribly fast, and so has to pass through a really wide pipe. Factory chimneys, on the other hand, are moving a much smaller volume of much warmer gas, usually combustion-product "flue gas". This is usually quite a lot hotter than ambient, so it rather wants to go up a chimney and doesn't need a wide one; you just need a nice long chimney, both to get a strong stack effect and to discharge the gas as high up as possible, to spread the pollution by dilution, as it were.
(Incidentally, The Secret Life of Machines addresses the stack effect in episode five, on central heating. And while I'm on the subject, the extraordinary documentary Fred Dibnah, Steeplejack features the titular working-class hero climbing hundreds of feet up a brick chimney and then perching on scaffolding that looks as if it were assembled by blind drunkards and knocking the chimney down by bashing bricks, one by one, into the flue. It has to be seen to be believed.)
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