Science desk
< January 2	<< Dec \| January \| Feb >>	January 4 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

January 3

Using the IUCN Red List

Hello, I've been struggling for half an hour with the Red List home page[1] trying to decide whether or not Prosthechea cochleata var. triandra is endangered, since it concerns the article I have just created concerning that subject. Could anyone who is familiar with that website (since I understand Wikipedia relies mostly on it for endangered species classification) help me search or search and tell me what they consider it (Least Concern, Vulnerable, etc.)? --♦♦♦Vlmastra♦♦♦ (talk) 00:11, 3 January 2008 (UTC) Edit: Let me be more specific: My message was:[reply]

No results were found for the criteria you specified:

Text search: Prosthechea cochleata var. triandra
Modifier: Exact phrase
Search in: Whole database
Results type: Standard
Taxa: Species

If these are correct, then the species you are searching for may not be in the database.

I changed the database, taxa, modifier, etc. extensively, to no avail. Taxa should be listed whether or not endangered (and in that case as Least Concern) so I don't think this means it isn't endangered, and since P. cochleata var. triandra has been considered endangered elsewhere I imagine it has been reviewed by the IUCN. I would like to use this source, so any help will be appreciated. I assume that I am not searching correctly because common genera such as Cattleya and Paphiopedilum were similarly unlisted, and I know for a fact that Paphiopedilum rothschildianum is endangered. --♦♦♦Vlmastra♦♦♦ (talk) 00:28, 3 January 2008 (UTC)[reply]

You can set the modifier to "Starts with" and enter the genus to see if any species of a given genus is listed. A number of Paphs are listed but not P. rothschildianum. There seem to be no Cattleyas or Prosthecheas listed. Alternatively, use the "expert search" which allows you to drill down through the hierarchy of taxa, e.g. Kingdom PLANTAE, Phylum TRACHEOPHYTA, Class LILIOPSIDA, Order ORCHIDALES, Family ORCHIDACEAE, Genus Paphiopedilum, etc. Bear in mind that "only" about 40,000 species have been assessed. William Avery (talk) 12:42, 3 January 2008 (UTC)[reply]

And also, just for plants, it may not have been assessed since 1997. See http://www.iucnredlist.org/info/faq#technical-1 William Avery (talk) 13:34, 3 January 2008 (UTC)[reply]

I had already tried the expert search, but, thanks anyways... I guess it was just wishful thinking. 40,000 species is of course a massive number, but when actually looking for a particular species, those numbers seem limiting. By the way, I meant P. sanderiana was endangered for a fact (although I understand P. rothschildianum is known only from ~~three~~ two sites, since one burned down recently). I notice P. sanderiana is also missing.--♦♦♦Vlmastra♦♦♦ (talk) 05:55, 4 January 2008 (UTC)[reply]

Body shape and structure

What, exactly, gives us (and other organisms for that matter) their shapes and structures? Why does every person (well, almost every person) have a nose in the middle of their face, two eyes, their arms where they are, all of their kidneys and other organs virtually the same shape and location, etc... I know its in the DNA, but could that answer be elaborated on? Thanks. --71.117.37.108 (talk) 03:34, 3 January 2008 (UTC)[reply]

If you don't know of it first see evolution.--Dacium (talk) 04:27, 3 January 2008 (UTC)[reply]

See also developmental biology, a whole scientific field devoted to these issues. --JWSchmidt (talk) 04:43, 3 January 2008 (UTC)[reply]

Another article that may be of interest is morphogenesis, which is the process by which our body forms shapes and structures. One of the most important genes in forming shapes and structures in the right place are the Hox gene family, which are turned on at different places along the length of a developing embryo thereby patterning the body plan. The pattern laid down by the Hox genes then turns on other genes which in turn start processes that form organs and structures. Its a very complex system in humans and we are a long way from fully understanding it, but by altering genes in animal models (especially fruit flies) and seeing the absence of wings for example, we begin to find the important genes and how they work. Rockpocket 04:57, 3 January 2008 (UTC)[reply]

Focal distance and light intensity (camera question about f-stop)

According to the f-stop article, a 135mm lens and a 100mm lens at f/4 transmit the same amount of light to the focal point despite the aperture being larger in the 135mm lens. How can this be? Something about a longer focal length reduces the amount of light that reaches the focal point but I don't see why this should be. When light is diverging from its source, I can see why being further away from the source would lead to a reduction in observed intensity but when the light is converging to a point I expect that the more light you begin with, the more light you have after converging. ----Seans Potato Business 12:03, 3 January 2008 (UTC)[reply]

Essentially true for point sources (such as a star), but most photographers are concerned with extended sources. Imagine using the 100mm lens at f/4 to take a picture of a white square (like a piece of paper). On the film or sensor, it images to a 10x10mm square. Switch to the 135mm lens at f/4, and, yes, more light is collected from the paper, but now it's spread over 13.5x13.5mm on the film or sensor. The exposure for a given pixel on the sensor, or "tiny patch" of film, is exactly the same. This is what matters for photographic exposure, not the total number of photons collected over the whole area of the white square. -- Coneslayer (talk) 12:47, 3 January 2008 (UTC)[reply]

Is it possible to make a 135mm lens that focuses down to a square of 10x10 instead of 13.5x13.5mm? Also, what if I had an SLR and swapped between 135mm and 100mm lenses - since the CCD is fixed in size, this madness will lead to either incomplete coverage of the CCD (wasting pixels of a 13.5x13.5mm CCD) or spilling picture off the edges of the CCD (so the outer parts of the image are not captured because the CCD is only 10x10mm (or whatever size it is)). ----Seans Potato Business 13:54, 3 January 2008 (UTC)[reply]

I think you misunderstand. I'm talking about the size of a particular object in the image, a sheet of paper. Not the coverage of the lens (how much of the CCD it illuminates). If you switch to a different focal length, of course the image of the piece of paper changes size on the sensor—that's why we use different lenses, so that we can control the size of objects that we image (a long-focal-length lens to make things big—like a small bird far away, or a short-focal-length lens to make things small, and encompass more of the scene—like a landscape). If your subject fills the frame with a 100mm lens, and you switch to a 135mm lens, why would you complain about it "spilling picture off the edges"? Why did you switch to a 135mm lens if you didn't want that to happen? -- Coneslayer (talk) 14:03, 3 January 2008 (UTC)[reply]

lol. 'Cause I don't know what I'm doing? *drops camera* - I understand it now. Thanks :) ----Seans Potato Business 14:08, 3 January 2008 (UTC)[reply]

Don't drop it—keep playing with it, so you get the hang of this stuff! You might check out Ansel Adams' The Camera (ISBN 0821221841) for a good explanation of photographic optics. It's not as warm and fuzzy as today's "Everything for Dummies" books, but is probably OK for the sorts of people who read this Reference Desk. -- Coneslayer (talk) 14:26, 3 January 2008 (UTC)[reply]

Lens focusing by eye

I was wondering, if I hold a glass lens in behind a window to the outside world and a piece of paper behind the lens, the focal length of the lens should be equal to the distance between the lens and the paper when the image is in focus. In actuality, however, wont there be some ability of the lens in my eye to compensate for poor focusing of the image, thereby creating a small range of paper-glass lens distances for which the image appears in focus? You might argue that, if this is the case, you can just take the middle of the range, but that assumes that the eye can focus from "neutral" (where the image on the paper really is in best-possible focus) to an equal extent in both plus and minus directions? ----Seans Potato Business 14:03, 3 January 2008 (UTC)[reply]

First, the statement that "the focal length of the lens should be equal to the distance between the lens and the paper when the image is in focus" is only true for a simple lens. For a complex lens like most photographic lenses, it's not really true. Second, if you're forming the image on a surface, like a sheet of paper, or the focusing screen of an SLR camera, your eye doesn't matter. The image formed is like ink on the page of a book. With something like binoculars or a telescope, you're not forming the image on a surface—you're looking at the "aerial image". In this case, you can compensate (to some extent) for the instrument's focus with your eye's focus. -- Coneslayer (talk) 14:08, 3 January 2008 (UTC)[reply]

When you talk about simple and complex lenses, is it that a simple lens focuses to a single point whereas a photographic lens must focus to a square? —Preceding unsigned comment added by Seans Potato Business (talk • contribs) 14:12, 3 January 2008 (UTC)[reply]

No, that's not the distinction. The simplest lens exists only in physics classes, like a spherical cow. That would be the "thin lens" that magically bends light, but has no thickness. You can see how that makes it easy to measure the distance from the object to the lens, and the lens to the image. A real simple lens is one that has only one element (piece of glass), like a magnifying glass. If you take a magnifying glass, you can see that you can produce an image of a light on a sheet of paper. If your light is big (like the overhead fluorescent fixture in an office, or a table lamp with a shade at home), you will see that it's not just covering a point—you can see the full shape of the fixture. A complex lens, like a camera lens, has multiple elements, in order to improve the quality of the images it produces (see aberration (optics)). First of all, they're big, which makes it unclear how, exactly, you would measure the distance from the lens to the image (from the front of the lens? middle? rear?). Second, many of them are of a retrofocus or telephoto design, which completely removes the direct relationship between lens-to-image distance and effective focal length. -- Coneslayer (talk) 14:21, 3 January 2008 (UTC)[reply]

I think the original poster's statement about "the focal length of the lens should be equal to the distance between the lens and the paper when the image is in focus" is only true if the objects you're projecting onto the paper are at "infinity" (+/- a smidge, of course). For closer objects, the relationship between the paper and the lens must shift. The lens of your eye is different because its curvature can be shifted by the muscles of your eye, changing its effective focal length.

Atlant (talk) 16:46, 3 January 2008 (UTC)[reply]

Yes, the distance from the simple lens to the image is only equal to the focal length if the object being imaged is very far away ("at infinity"). Otherwise, the distance from the lens to the paper increases according to the thin lens formula. -- Coneslayer (talk) 16:52, 3 January 2008 (UTC)[reply]

If I understand correctly, you're asking if the lenses in your eyes can compensate for a blurry image projected onto a piece of paper, or, for that matter, printed on one. They can't. If you focus exactly on the image, it will look however blurry it is. If you don't, it will look blurrier. The best way I can think of to explain it is that once the image is projected onto the paper, the information about which way the light came from is lost. — Daniel 20:15, 3 January 2008 (UTC)[reply]

Excessive emotional responses

Children seem to be more aware of and responsive to their emotions, sensations and feelings. E.g. they laugh / cry more readily. Why is this and is there a term or article about it? Is it a lack of something or too much something? - CarbonLifeForm (talk) 14:39, 3 January 2008 (UTC)[reply]

Bear in mind it is a very complex process of going from being a child to becoming a fully developed adult, especially in regards to the amount of nervous branches in the brain in this case. Everyone has a fear of the unknown, and a child who has learnt little with be more easily overwhelmed by what they experience than an adult would, because they haven't seen a lot of it before. As far as I know there is no article on children's emotional development, but for further reading you could use this site: Erikson's Eight Stages of Development Cyclonenim (talk) 14:50, 3 January 2008 (UTC)[reply]

Children have a more labile affect. MrRedact (talk) 14:53, 3 January 2008 (UTC)[reply]

What is this object?

Can someone identify this object (two pictures are below). It is made of metal, it is almost as big as a football. It is about 8 inches high. I could get more measurements of it and weigh it, if that would help.

photo 1 photo 2 Bubba73 (talk), 16:02, 3 January 2008 (UTC)[reply]

It looks like a meteorite to me. Is that speculation consistent with the object's history?

Atlant (talk) 16:41, 3 January 2008 (UTC)[reply]

I think it looks like a clinker. (Altho, we don't have much of a good article on the type of clinker I mean.) I found something similar as a kid and thought it was a meteorite too. Friday (talk) 16:50, 3 January 2008 (UTC)[reply]

(To me, it seemed awfully large to be a clinker, although battling that one would certainly do the old man proud!)

Atlant (talk) 19:33, 3 January 2008 (UTC)[reply]

Well, the thing I found as a kid which I was told was a clinker (meaning, basically, a big rock-like cinder) was probably about football sized. I always assumed the cinder explanation was right, but I suppose I have no way of knowing this for sure. A couple older people I showed it to seemed to think it looked like a normal thing they had seen before. It looked like a bunch of rock and/or metal, all melted together, and full of weird holes. Friday (talk) 19:47, 3 January 2008 (UTC)[reply]

Looks like an ironstone concretion - basically a weathered rock like sandstone where the iron in it has become concentrated along joints or fractures. It is common for such concentrations to be sub-circular, as the iron sort of filters out from a central point. Cheers Geologyguy (talk) 16:55, 3 January 2008 (UTC)[reply]

I agree. It looks very much like one. There are such "things" around here (Southern New Jersey). I say "things" because they aren't really rocks. Ours are formed straight from sand, not sandstone. They are surprisingly heavy and can be any size. Some of them even form pipes or tubes. --Milkbreath (talk) 21:05, 4 January 2008 (UTC)[reply]

Try breaking it open. If you succeed show us a photo of the inside. Theresa Knott | The otter sank 17:29, 3 January 2008 (UTC)[reply]

I don't think there is any way for me to break it open - it is very solid. My father thought it was a meteorite, but I don't think it is. This one and a larger, similar one were both found in a hole in some river sand in south Georgia. I haven't seen anything quite like them around here, and I don't know of any local industry where they would be waste products. I haven't checked its magnetic properties, but it seems to be iron. I think it is unlikely to be a meteorite, since two of these were found in a hole.Bubba73 (talk), 18:17, 3 January 2008 (UTC)[reply]

I bet if you try a magnet on it, you'll find it is not magnetic. The metallic iron-looking stuff is not iron, per se, but iron oxide, the result of weathering. Cheers Geologyguy (talk) 18:48, 3 January 2008 (UTC)[reply]

Iron oxide not magnetic? [[2]]--TreeSmiler (talk) 01:50, 4 January 2008 (UTC)[reply]

Sorry, magnetite is an iron oxide that is magnetic, but this is probably not magnetite. I think it likely that the iron oxides in this rock are hematite, limonite, goethite and the like, none of which are magnetic (at least not attracted to a magnet). See also Bog iron. Thanks for nudging me to make the clarification. Cheers Geologyguy (talk) 01:55, 4 January 2008 (UTC)[reply]

It appears that Goethite becomes magnetic in a reducing flame. Is this one test that could be done on a small sample?--TreeSmiler (talk) 02:22, 4 January 2008 (UTC)[reply]

You would need a blowpipe and alcohol burner to do it right - the times I tried such tests were abysmal failures. Takes a pretty delicate touch. Cheers Geologyguy (talk) 15:54, 4 January 2008 (UTC)[reply]

In case any readers are puzzled by the blowpipe reference, we have an article at Blowpipe (tool). DuncanHill (talk) 15:58, 4 January 2008 (UTC)[reply]

A hole like someone might dig for a fire? I still think it's a cinder. Friday (talk) 18:54, 3 January 2008 (UTC)[reply]

It was a deep hole - 6 or 8 feet. It was hard for them to bring them up. I think it is far too heavy to be a cinder. Bubba73 (talk), 19:49, 3 January 2008 (UTC)[reply]

Looks like clinker (furnace waste) especially because of the black glassy bits.Polypipe Wrangler (talk) 08:09, 7 January 2008 (UTC)[reply]

OK, but what kind of furnace or factory? There is no furnace that I know of near there. Of course, it could have been carried a long way and discarded there, possibly. Bubba73 (talk), 03:13, 8 January 2008 (UTC)[reply]

ISO setting verus shutter speed

If you go here and scroll down to the example pictures, Film_speed#Digital_camera_ISO_speed_and_exposure_index... where they say they change the "ISO setting", do they mean they changed the film inside the camera? If not, what is the difference between the ISO setting and the shutter speed? --Seans Potato Business 16:14, 3 January 2008 (UTC)[reply]

Digital cameras don't have film inside. --LarryMac | Talk 16:19, 3 January 2008 (UTC)[reply]

To expand on that a little... The only way to change the ISO sensitivity of a film camera is to open it up and put different film inside. The sensor of a digital camera, on the other hand, is capable of acting like film of several different ISO sensitivities, so you can change it at the push of a button. (I think it changes the gain of the internal analog-to-digital converter). —Keenan Pepper 16:27, 3 January 2008 (UTC)[reply]

(ec) The 'shutter speed' is simply the amount of time the film (in a film camera) or image sensor (in a digital camera) is exposed to light when taking a picture. 'Shutter speed' and 'exposure time' are synonyms. It's easier to hold the camera steady for a short exposure than for a longer one, and moving objects in the scene will be less blurred. Longer exposures will be required for dimly-lit subjects (indoors, night shots, etc.).

The 'ISO setting' on a film camera is a mechanism (usually a knob) that lets you dial in the sensitivity of the film. (You may also see 'ASA setting' on older cameras; it does the same thing.) The camera needs to know how 'fast' or 'slow' the film is that has been loaded so that it can calculate appropriate exposure times. 'Faster', more sensitive films require shorter exposure times but also tend to appear grainier and have poorer colour saturation.

For a digital camera, one (obviously) can't change the film. Instead, the ISO setting adjusts the sensitivity of the sensor that captures the images. Once again, choosing a higher ISO setting (more sensitivity to lower levels of light) allows one to set a shorter exposure time, but this comes at a cost of 'noisier' images. In principle, a scene shot at ISO 100 and an exposure time of 1 second should be of equal brightness in the recorded image as the same scene shot at ISO 1600 and an exposure time of 1/16 of a second. The former image will be more prone to motion blur, while the latter will be grainier (film) or noisier (digital). TenOfAllTrades(talk) 16:30, 3 January 2008 (UTC)[reply]

So the difference in brightness observed in the example in that article, is due to disparity between the ratio of the two ISO settings and the ratio the shutter speeds? Ideally, shouldn't the photographer, if they intended to use those photos in that article, have used a 1/5600 shutter speed (perhaps not possible on the camera used) in order to show the similarity? --Seans Potato Business 17:19, 3 January 2008 (UTC)[reply]

Yes, it would absolutely be better (for the clarity of the article) to do as you suggest. The camera used has a fastest shutter speed of 1/4000 second, so shooting at 1/5600 would not be possible. However, shooting at a smaller aperture would have made it possible to do what you suggest. At f/8 (one stop smaller), the shutter speeds would have been 1/175 and 1/2800. -- Coneslayer (talk) 17:26, 3 January 2008 (UTC)[reply]

One could, if it wasn't considered "dishonest", take a copy of one photo, maybe change it ever so slightly, and then say that it is the same subject with both shutter speed and ISO changed by the same ratio? Alternatively, if it's not too much hassle, perhaps you could take suitable photographs? I don't yet have a suitable camera. --Seans Potato Business 01:02, 4 January 2008 (UTC)[reply]

Yeah, maybe I can do it this weekend. I have a Pentax K10D that will do the trick, and it's fairly noisy at ISO 1600. Usually, that's not such a good thing, but I guess for this application, it is. -- Coneslayer (talk) 01:10, 4 January 2008 (UTC)[reply]

Thanks, Coneslayer. No, SPB—'doctoring' a photo to show a specific effect is definitely 'dishonest'. It's the sort of thing that gets academic types suspended or expelled (if students) or fired and blackballed (if faculty). TenOfAllTrades(talk) 15:17, 4 January 2008 (UTC)[reply]

Yeah, but I'm not suggesting it to support scientific research! I would never! I simply suggested it for educational purposes and don't think it's nearly as immoral... --Seans Potato Business 18:06, 4 January 2008 (UTC)[reply]

But we're an educational resource. (At least, we're trying to be.) Faking the data and lying to our readers isn't really a business we want to get into. Besides, are you sure that you would add the correct type(s) of noise to the image? Not all noise is created equal, and understanding it (and simulating it) properly is a non-trivial task. (Compare shot noise, salt and pepper noise, Gaussian noise, thermal noise....) TenOfAllTrades(talk) 19:08, 4 January 2008 (UTC)[reply]

I don't think lying is inherently bad. People do it all the time. You ask someone if lying is bad and they scream "YES!!", but then I ask what's Santa Clause? It's a lie! People lie all the time in some perfectly moral (and immoral) ways. I think it's the malicious intent behind a lie that makes it bad. If I was educating a class of children and needed to illustrate a point, my focus would be on the ideas that they walked away with, not how I managed to get those ideas across. The technical issue that you raise is however quite valid, I suppose. Do noise patterns vary between cameras? --Seans Potato Business 00:33, 6 January 2008 (UTC)[reply]

Coneslayer: I already uploaded photos for the article; the photos were taken using my Nikon D40x DSLR at ISO 100 and ISO 3200. If your photos are more encyclopedic, feel free to replace my images with them. --Bowlhover (talk) 19:33, 5 January 2008 (UTC)[reply]

(Thanks for updating the images) Was your camera mounted on a tripod? If so, why the blur on ISO 100? --Seans Potato Business 00:24, 6 January 2008 (UTC)[reply]

No, I didn't mount my camera on a tripod. I wanted to use motion blur to show the exposure time is longer on ISO 100 than on ISO 3200, since motion blur is the only reason not to shoot at the lowest possible ISO. --Bowlhover (talk) 03:12, 6 January 2008 (UTC)[reply]

What about noise? We were expecting a crisp ISO 100 and noisy 3200. --Seans Potato Business 11:37, 6 January 2008 (UTC)[reply]

indian resources on iron

tell about all indian resources of iron —Preceding unsigned comment added by 210.89.50.190 (talk) 17:42, 3 January 2008 (UTC)[reply]

Do you mean: "Where is iron being mined in India?" -- kainaw ™ 17:56, 3 January 2008 (UTC)[reply]

By googling "indian resources of iron" I got this link [3]. Maybe that's useful. --Taraborn (talk) 08:55, 5 January 2008 (UTC)[reply]

Falling Leaf

Is there a name for the side to side motion a leaf makes when it is falling to the ground? --Juliet (talk) 19:56, 3 January 2008 (UTC)[reply]

I don't know that there's a particular name for it, but it looks like someone's studied it. (It looks like they call this particular motion "fluttering". I don't know if other people would associate that word with this specific motion.) -- Coneslayer (talk) 20:01, 3 January 2008 (UTC)[reply]

I am writing a presentation

Can you please answer a couple questions for me please? —Preceding unsigned comment added by 207.69.139.157 (talk) 22:25, 3 January 2008 (UTC)[reply]

Maybe. Ask specific questions on specific topics (after having searched wikipedia yourself to get your feet wet, obviously) and we'll see what we can do. DMacks (talk) 22:36, 3 January 2008 (UTC)[reply]

Kidney in hagfish

I'm confused as to what "type" of kidney an adult hagfish has? I guess it's safe to assume that at the larval stage it's a pronephros, but does it change to a mesonephros at a later stage? Wikipedia says that pronephros is an active organ in the adult hagfish and my book (Introduction to Chordatezoology by J. M. Jørgensen) says that in 'some' hagfish the pronephros will turn into a bloodcreating organ, 'like' mammalian bone marrow, thus making it an active organ but not the active kidney? And I've always been told that all "higher" chordates (so everything other than urochordates and cephalochordates) develop a mesonephros, however i've also been told that only amphibians and fish have a mesonephros as the adult kidney, so which is it? 80.63.191.67 (talk) 23:23, 3 January 2008 (UTC)[reply]

Battery effect

I know from radio-controlled models that if you empty certain rechargeable batteries (I'm pretty sure it is nickel-cadmium batteries) in a short time until the model won't drive or fly any more, then wait a few minutes, then the batteries can be used again for driving/flying for a short time. It may appear as if the battery would recharge itself partially. I think this effect is due to the thermochemistry of the discharge reactions, i. e. they lower the entropy (and lower the enthalpy, else the reaction wouldn't occur at all) so that the chemical equilibrium is shifted towards the charged state at higher temperatures. Any further thoughts on this? Icek (talk) 23:28, 3 January 2008 (UTC)[reply]

Maybe the cells cool down causing a lowering of their internal resistance giving you more current capacity when you re energize? See Nickel cadmium--TreeSmiler (talk) 23:36, 3 January 2008 (UTC)[reply]

But the article claims the opposite - "This meant that as the cell temperature rose, the internal resistance fell". Icek (talk) 22:26, 4 January 2008 (UTC)[reply]

Yes well spotted. I missed that bit (with it being hidden away in the 'disadvantages' para.) Im not sure if its true though as there doesnt seem to be a ref to that effect and i have not heard of it before.--TreeSmiler (talk) 01:57, 5 January 2008 (UTC)[reply]

I'm fairly sure this is the surface charge (an electrical charge stored in the metal of the battery, similar to that of a capacitor) that you're encountering: the chemical reactions that drive the battery run at a limited rate, and when you've nearly drained the battery, they can't go fast enough to generate a usable voltage/current. If you let the battery sit, however, the reactions will keep running until they rebuild the surface charge, which gives the appearance of a partial recharge. --Carnildo (talk) 00:24, 5 January 2008 (UTC)[reply]

Flash evaporation of a solution

If you were to flash evaporate a liquid with a solid dissolved in it, e.g. sugarwater, would the solute not have time to crystallize and just turn into an extremely fine powder? Would it be separated into individual molecules? Would it matter of the solute was disassociated, e.g. saltwater? — Daniel 23:51, 3 January 2008 (UTC)[reply]

Did you see the paragraph on Spray drying therein? Your conclusion is right, you will get a fine powder. With sugar if you do it slow enough you will get a supersaturated syrup which could make a sticky foam that gums up your system. The ions in a disassociated ionised soltion will make the effort to recombine into a salt powder. You want get a plasma of sodium and chloride ions unless you do it at an extreme temperature! Graeme Bartlett (talk) 03:33, 4 January 2008 (UTC)[reply]

How fine will the powder be? It seems like spray drying would result in crystals forming in each individual droplet, and result in a powder that isn't as fine as would be created with flash evaporation. — Daniel 07:44, 4 January 2008 (UTC)[reply]

As the first few words of the article will tell you, flash evaporation is partial. It will leave you not with a powder but with a cooler, possibly supersaturated liquid. --169.230.94.28 (talk) 17:05, 4 January 2008 (UTC)[reply]