Wikipedia:Reference desk/Archives/Science/2006 November 18

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1 November 18

[edit] November 18

[edit] note

the actions of refdeskbot appear to be hiding certain edits from the edit history annoyingly - I've left a message for the operator. This didn't use to happen (everything was better in the old days). Please delete this message one problem is resolved..—Preceding unsigned comment added by 87.102.21.223 (talk • contribs)

Message left at user's talk page in response. This is normal behavior for the bot, but is, I'm sure, open to some forms of discussion. M a rtinp23 00:38, 18 November 2006 (UTC)

I've left a message on your talk page. Suggesting archiving stuff that does not appear on the main (current) page. Current bot behaviour is wrong - if material on the main page is edited it should appear in the main page edit history.

Please see http://en.wikipedia.org/wiki/Wikipedia_talk:Reference_desk#refdeskbot Thanks87.102.21.223 01:04, 18 November 2006 (UTC)

[edit] The Moon

Is there anyway way to find out what some resources on the moon might be and how much of them is there? I checked the article if it's there I missed it.67.126.131.137 01:58, 18 November 2006 (UTC)

Is rock a resource? How about vacuum? --Wirbelwindヴィルヴェルヴィント (talk) 04:10, 18 November 2006 (UTC)

It depends on what you mean by resources. If you are talking about water, there is a smal possibility that some water ice exists in the permanently shadowed areas of large polar craters. Other than that, it depends what you need. All the chemical compositions or roacks and such are discussed in the main article. pschemp | talk 04:46, 18 November 2006 (UTC)

See Moon. StuRat 04:40, 18 November 2006 (UTC)

Ah I overlooked composition but one more thing, Which of these elments could be used as radiation shielding?

Lunar regolith has a number of uses. Since it's primarily made of oxides, there's potential for it to be used for in-situ oxygen generation. Some research has calculated that about 1-2 meters of regolith will provide ample shielding from radiation PDF. And apparently it can be utilized for a sort of concrete (like any rock mixture, I suppose). A good site to check out would be NASA's Centennial Challenges - there's a few there devoted to regolith mining and utilization. (Disclaimer: I'm involved in a team working on one of them) Virog^{It's not}_{my fault!} 07:55, 18 November 2006 (UTC)

The best evidence indicates Wensleydale as a major resource. B00P 08:56, 18 November 2006 (UTC)

As for radiation shielding, pretty much anything will do provided you have enough of it, though as I understand it hydrogen or simple hydrocarbons such as polyethylene are the best for cosmic ray protection on a mass-constrained spacecraft, and, unfortunately, hydrogen is very, very rare on the moon. But if you're building a static radiation shield on the moon itself, just pile up the moonrock as is. It'll be fine for the job. --Robert Merkel 10:37, 18 November 2006 (UTC)

Thank for all the information, Wensleydale sounds good.

I have read research saying that the lunar dust is similar to Portland cement, in that if you mix it with water it sets up like concrete. If water were extracted from the polar region, structures could be build in situ which would provide radiation shielding and protection from meteor impact, much cheaper than bringing structures and building material from Earth. There is also abundant solar energy (never a cloudy day).Edison 21:55, 18 November 2006 (UTC)

[edit] Highest and lowest temperature and pressure

What is the highest temperature that could be obtained artificially? What is the highest pressure that could be obtained artificially? What is the lowest temperature that could be obtained artificially? What is the lowest pressure that could be obtained artificially?

Thank you.

For low pressure, see Ultra high vacuum, and even though you didn't specifically ask for low temperature (you asked for high temperature twice), see absolute zero for that. —Keenan Pepper 05:14, 18 November 2006 (UTC)

High temperatures and pressures are obtained in explosions - a nuclear explosion would probably be the best. That may not be useful. Alternatively for high pressure you could try Diamond anvil cell. For high temperatures you could try "electron beam furnaces" see http://www.theodoregray.com/PeriodicTable/Stories/077.x3/ . I don't know if these are the hottest but it's a good place to start. oxy-acetylene torches also get hot - about 3500 c according to wikipedia.

Experimental fusion plants are contenders for both highest temperature and pressure. You should also consider trying to find out what temperature the movement of the accelerated particles in particle accelerators is equivalent of, as temperature basically just is "average movement of molecules" and particles in a particle accelerator reach incredibly high speeds. TERdON 03:30, 18 November 2006 (UTC)

So light is the hottest thing in the universe? :) Or maybe tachyons, they are even faster (if they do exist). --V. Szabolcs 20:38, 18 November 2006 (UTC)

Only random, isotropic thermal motion counts as heat; other motion (such as that of photons or uniformly-accelerated particle beams) doesn't count. Temperatures are only assignable to collections of objects in thermal equilibrium, but you can even do that for photons. Original questioner: see negative temperature; oddly enough, such temperatures can exist and are, in some sense, hotter than all normal positive temperatures. Obviously temperature and pressure are bounded from below by 0 (remembering that negative temperatures aren't below 0!); do you really mean could be obtained, or is practical to obtain? If the latter, then look at cryogenics and vacuum. --Tardis 21:01, 20 November 2006 (UTC)

[edit] Known black holes

What is the number of known black holes in the universe?

I don't personally understand astronomy very well, but after a Google search, it seems that there have been 300 identified sources of gamma rays, which black holes are believed to spew out. 100 of these black holes are are the "brightest supermassive" ones of the bunch, found in other galaxies. It's believed that there are millions of black holes, but this gamma ray detection observatory has found 300. [[1]] -Chickenflicker 04:15, 18 November 2006 (UTC)

Depends what you mean by "known". We don't really know any black holes exist, because general relativity could break down under those conditions. —Keenan Pepper 05:18, 18 November 2006 (UTC)

There's a lot more than three hundred. Pretty much every quasar/blazar out there is presumed to be driven by a supermassive black hole - I have no idea what the current catalogue is, but it's fairly large. Galaxies without AGN can still have supermassive black holes at the center, as well (such as ours), and there's lots of those. And then there's all the smaller black holes that can be found in a single galaxy - I think there have been a few "directly" observed in the past year or two, but I forget when/where. But as far as absolute confirmation of what we think is a black hole, Keenan has a point. All we can really see is the effect of something really massive that's compact and doesn't emit light (aside from jets/accretion disks). Virog^{It's not}_{my fault!} 08:04, 18 November 2006 (UTC)

[edit] Number of body cells

What is the total number of body cells?

"[H]umans have an estimated 100 trillion or 10¹⁴ cells." See Cell (biology). Why is there a blue dotted line box around my text? 68.112.172.251 04:02, 18 November 2006 (UTC) (Chickenflicker, not logged in)

Cause you have a leading space. --Wirbelwindヴィルヴェルヴィント (talk) 04:08, 18 November 2006 (UTC)

Many thanks. Chickenflicker---♣ 04:24, 18 November 2006 (UTC)

Well, that's a very rough estimate. According to [2], some sources estimate the number of cells as 10 trillion. So I think the actual number is somewhere between 10 and 100 trillion cells. --Bowlhover 04:04, 18 November 2006 (UTC)

That's a pretty rough estimate as well, haha. Chickenflicker 04:05, 18 November 2006 (UTC)

Yup, these kinds of things are very difficult to estimate. You can't just take a human, take a microscope, and start counting the cells. --Bowlhover 05:45, 18 November 2006 (UTC)

Since everyone has a different sized body there is a lot of variation. But how hard could it be to get an estimate of the number of cells in a body - surely if you know the size of all the different tissues and the number of certain cells per amount of volume you can calculate it. I didn't word that last sentence well but ah well --WikiSlasher 12:08, 18 November 2006 (UTC)

Funny, I asked myself this question just yesterday and made a quick calculation. Assume one cell is 1 mm across and a human has a volume of 1 m³, then there are 1000³ = 1 billion cells. The human body is somewhat smaller, but cells are a whole lot smaller, so I guessed the number would have to be several orders of magnitude greater. However, the cell (biology) article says there are about 100 billion cells, considerably more than I guessed. The average cell must be less than 0.1 mm across.

Btw, the reason I asked myself this is that I wanted to have an idea of which lifeforms constituted the most cells on Earth. Form the numbers in the species article one may conclude that there are several times more species of bacteria than all other lifeforms put together. And given their size, there are probably more individuals per species than for bigger species, so they probably outnumber the rest in that respect too (anyone know this?). But what about biomass? So I decided to look at the number of cells. Assuming there are 5 billion humans with 100 trillion cells then together they have 5 × 10²³ cells. The bacteria article says "The number of Bacteria in the world is estimated to be around five million trillion trillion, or 5 × 10³⁰. So bacteria constitute a 10 million times more cells than humans. And how many cells do the other species constitute? There are only a few million species, so the bacteria still win easily. And that's not even taking into consideration that humans are a rather big and numerous species. Before I assumed that the one would compensate for the other, but humans are much more numerous than one would expect for our size. So I must conclude that this world still belong to the bacteria. All other lifeforms put together are vastly outnumbered in all respects. Sorry about the elaboration. Just having some fun with myself. :) DirkvdM 13:57, 18 November 2006 (UTC)

Even within the human body, bacterial cells far outnumber human cells (by number, but not by volume). Just something to think about. Tuckerekcut 16:33, 18 November 2006 (UTC)

Indeed, one millimeter is far too large for a cell’s diameter—if that were so, individual cells would be visible to the naked eye, and with a magnifying glass, you’d be able to make out organelles. The ovum is the largest human cell and is probably about 0.1 mm across, but I’d say the average human cell is probably only about 0.01 mm in diameter. But yes, bacteria easily win. — Knowledge Seeker দ 20:28, 18 November 2006 (UTC)

Oh, and I was not even counting the mitochondria. Most living things have a baterium in every cell (a cell within a cell). DirkvdM 09:28, 19 November 2006 (UTC)

[edit] Fish bones?

Why do some fishes have many very tiny bones while others have only a few large bones? Is there an evolutionary theory that explains the fish bones? -- Toytoy 03:31, 18 November 2006 (UTC)

The most obvious explanation is that small fish have small bones and large fish have large bones. StuRat 04:32, 18 November 2006 (UTC)

If small fish had large bones, they wouldnt be able to fit them all in. And if large fish had only small bones, they would be too floppy. 8-)--Light current 17:27, 18 November 2006 (UTC)

Its all a matter of fish scale 8-)--Light current 17:28, 18 November 2006 (UTC)

And different types of bones often serve different purposes. --24.147.86.187 05:35, 18 November 2006 (UTC)

Differing evolutionary lineages.
B00P 08:59, 18 November 2006 (UTC)

As I know those little "bones" are not bones at all. (they are from some other material the bones are from) However, I don't know why some species have none of them and have only the vertebral column. --V. Szabolcs 20:31, 18 November 2006 (UTC)

The morphology of fish skeletons is related to function. I can't tell you details of what skeletal adaptations are necessary for what lifestyle, but I do know that very fast-swimming fish (eg. tunas), medium-speed fish (eg. trout and salmon), and slow-swimming fish (eg. crappies) will have different skeletal structures. The tunas seem to have rigid "ribs" extending from the vertebrae; the salmon seem to have lots of little bones lining the gut cavity. I've never cut up a crappie so I couldn't tell you about them. --Ginkgo100 ^{talk · e@} 15:14, 19 November 2006 (UTC)

[edit] Capacitance problem

This is another one of those "find the equivalent capacitance" problems that are common among physics students' homework. However this one is slightly different as it cannot be immediately reduced by the rules for series and parallel capacitors. The circuit consists of four junctions, a through d arranged in a square, such that:

The potential difference is applied across a and b, which are at opposite vertices.
Capacitors are connected between a and c, b and d, and c and d.
Wires link ad and bc.
There are no other connections.

Google and the relevant Wikipedia articles aren't very helpful. Please show me how to reduce this circuit into something I can easily deal with using the formulae for series and parallel capacitors. Thanks. MER-C 09:17, 18 November 2006 (UTC)

Interesting - assuming the wires have negliable resistance then the voltage difference across bc and ad should be zero, therefore the voltage across cd is the full potential difference. Therefore if a is at +v, b at -v, then c is at -v, d at +v. This gives the voltage across db = 2v ie the full potential difference. The same applies for the capacitor ac. The result is all three capacitors see the same voltage - this is the same as having capacitors in parallel. so the total capacitance is the sum of there capacitances. (Somebody please check this to be correct)

I concur, I got 3 capacitors in parallel with some voltage source.

I've got it. Thanks for the help! MER-C 05:37, 19 November 2006 (UTC)

[edit] Power Voltages

Why are the Voltages in 50 Hz. AC system always a multiple of number 11 (eleven) such as 220kV, 132kV, 66kV, 33kV, 11kV etc.. Adilmohiuddin 10:00, 18 November 2006 (UTC)Adil

Also 475 kv, 440V etc. I asked this question a few months ago. I dont think I got an answer! 8-(--Light current 17:23, 18 November 2006 (UTC)

Are you certain that they are at the first place? Here in Sweden, we switched a couple of years ago from 220 volts for household use to 230 volts, as I understand the latter is the European standard.... \Mike (z) 19:43, 18 November 2006 (UTC)

Yeah were not talking LV really. More like distribution voltage levels 8-)--Light current 20:03, 18 November 2006 (UTC)

It's probably because it's really a multiple of a base voltage. Is 11kV the smallest distribution voltage? If so, the step up transformers are just integer multiples of that. 11kV isn't magic, it's just that whatever votage is picked first, all subsequent voltages will probably be a multiple of that. As for the low voltage, there are multiple taps at least in the U.S. 110/220 for houses, 110/208 and 277/480 for commercial/industrial. --Tbeatty 23:49, 18 November 2006 (UTC)

Hmmm. Not convinced. Isnt (wasnt) 6.6kV used as well?--Light current 11:21, 19 November 2006 (UTC)

The "simple transformers" argument still works with 6.6kV, as it is a simple step down from 11kV (winding ratio 11:6) -- AJR | Talk 19:19, 20 November 2006 (UTC)

10:6 (or 5:3), AJR. 11:6 on 11 would give, um, 6. --Tardis 20:44, 20 November 2006 (UTC)

[edit] Sunlenses

Do suncontact-lenses (as in sunglasses) exist? Do they have them in 1 way mirror style? If not why? Keria 10:01, 18 November 2006 (UTC)

That would look cool. :) In Gangs of New York there is this guy with a glass eye with a bald eagle etched on it. At one point he even taps it with a knife ('ting ting'). I assume the actor was wearing 'lenses'. Sun-contact lenses make sense to me. One reason they might be difficult (ie expensive) to make is that you can't make them from just any material - it has to be easy on the eyes (literally). And the mirror version might look really freaky, so low sales, so again high price, I assume. DirkvdM 14:14, 18 November 2006 (UTC)

You can do all sorts of things with contacts now. Look at this, for example. Yeek! --jpgordon^∇∆∇∆ 15:20, 18 November 2006 (UTC)

I don't think they would be safe. Those with a fixed level of shading would be dangerous because you would be blind when you went into a low light area and you can't just take contacts off quickly like you can with sunglasses. Photosensitive lenses, which darken when the light level goes up, are a possibility. However, the sunglasses I've seen that do this react too slowly. So, while driving, if you caught the glare from the Sun's reflection off a windshield, you would then be completely blind for several seconds after the glare ended, until the contact lenses returned to their lower shading level. In those seconds, you may very well get into a serious accident.

Perhaps there would be a few cases, with a universally high illumination level, where shaded contacts might make sense. Skiing comes to mind, but shaded ski goggles could also protect the eyes from snow, ice, and cold, dry air. StuRat 22:13, 18 November 2006 (UTC)

Nike makes some, they're calle the Nike MaxSight. I would imagine that they would be less dangerous than a tinted windshield or even sunglasses, as light can't leak in from the sides constricting your pupil while they still need to look through shades. You would need some pretty stong shading to, in any circumstance, be made "completely blind for several seconds", I don't think that is likely. Tuckerekcut 23:37, 18 November 2006 (UTC)

In cases where there is an extreme diff between low and high light intensities, like driving at night, you can barely see anything other than headlights, as is. You wouldn't need to add much shading to make it impossible to see someone crossing the street wearing dark clothing. StuRat 00:28, 19 November 2006 (UTC)

[edit] Do animals have the period?

I have never seen a bloodened dog due to that. Thanks. —Preceding unsigned comment added by 85.50.35.112 (talk • contribs)

Please sign your posts with four tildes ~. Edison 06:24, 19 November 2006 (UTC)

They may do, but animals generally mate when they are in season. Dogs only come into season twice a year (and Dingos once), so it would be very uncommon for them to have a period if they had one, and it would probably be too small to see it. --liquidGhoul 13:58, 18 November 2006 (UTC)

Hmm, this is a bit of a girlie thing and here is another guy answering, but I believe only pregnancy will prevent menstruation. Just mating won't help. Period. DirkvdM 14:20, 18 November 2006 (UTC)

Depends on the species. Cats don't ovulate until they mate -- so a virgin female will stay in heat a long time. Cats in heat (those not intended for breeding, anyway) usually don't stay that way for long, though; they either manage to escape and find some cute boys, or their owners get fed up with their obnoxious calling and have them spayed. --Ginkgo100 ^{talk · e@} 15:08, 19 November 2006 (UTC)

Oh, and ever noticed how dogs lick their behinds? This might be one reason. Funny this comes up. I'll be having black pudding for dinner in an hour or two. Yummy! DirkvdM 14:21, 18 November 2006 (UTC)

the difference here is menstruation, ("having a period") vs. oestrus ("going into heat"). Humans, some other primates, bats, and shrews menstruate; other animals, including dogs, have estrous cycles. Details, including some specific to dogs, are covered in the latter article. - Nunh-huh 14:50, 18 November 2006 (UTC)

Friend of mine had some bitches once. He said thay used to bleed over the carpet. 8-(. Could be to do with whether they had been spayed or not. --Light current 15:57, 18 November 2006 (UTC)

I remember seeing a National Geographic documentary, where they visited the zoo in Antwerp,Flanders. The female people who worked with the monkeys had noticed that after a while, their own periods became synchronized with those of the female monkeys! Can you believe that?!Evilbu 16:10, 18 November 2006 (UTC)

Yes. Pheromones ?--Light current 17:11, 18 November 2006 (UTC)

I believe cats and dogs don't experience periods unless they live with humans. There are diapers for them designed for their periods, but they're usually not in great amounts. I believe it was also "Consequences of a long-term raw food diet on body weight and menstruation" that talks about women who eat a strict diet will also be rid of their menstuation cycles, such as a wild cat or wild dog would. --Wirbelwindヴィルヴェルヴィント (talk) 17:37, 18 November 2006 (UTC)

For example, see Menstruation - Is it Really Necessary or google search for "menstruation diet human unnatural raw". --Wirbelwindヴィルヴェルヴィント (talk) 17:41, 18 November 2006 (UTC)

For the actual facts, please consult the articles I mentioned above, especially estrous cycle. Neither dogs nor cats menstruate. Some dogs or cats may have occational bloody vaginal discharges, but not all do, and they are not equivalent to menstruation. - Nunh-huh 17:45, 18 November 2006 (UTC)

Yes, dogs come into heat every 6-9 months there is blood. I would call this menstruation but maybe not a period depending on the use of the term. --Tbeatty 23:52, 18 November 2006 (UTC)

If it happens periodically, the term 'period' seems appropriate. DirkvdM 09:31, 19 November 2006 (UTC)

Isn't bleeding a sign that your dog is in heat? --liquidGhoul 15:21, 19 November 2006 (UTC)

[edit] Data Tables

Hi, I'm doing a science fair project. And I need to make a data table, but I need some help. Could you make an example. It is a project about ants and what foods they like to eat. The different foods are sweets,carbohydrates,water,and proteins. Water is the control and the food are the variables. What would be the depent variables? What can of data table would I use? How I make the data table. Any suggestions on how to improve the project? Thank a lot. - Mrs. Lellek

Oh, Mrs. Lellek, how many years have you been married? Try reading line chart, dependent variable, and independent variable. X [Mac Davis] (DESK|How's my driving?) 21:27, 18 November 2006 (UTC)

How about something like this:

FOOD
CONSUMED
PER
ANT
(mg)
 ^                      # SWEETS 
 |             #
 |        #
 |     #                o CARBS
 |   #        o
 |  #   o
 | # o 
 |#o 
 |o@@@@@@@@@@@@@@@@@@@@@@ PROTEIN
 +----------------------->
  WATER SUPPLIED PER ANT (ml)

Of course, I just made up the graph, your actual data would need to be filled in. StuRat 21:56, 18 November 2006 (UTC)

Do you have a hypothesis you are testing in your experiment? And have you already collected your data? The form of the tables will depend on that. A month ago there was some discussion of a similar science fair project (but not of the data table set-up) at the Refrence desk, which you find archived here. --Lambiam ^Talk 22:53, 18 November 2006 (UTC)

The reference Lambliam gave is worthwhile rereading. Your independent variable is what you are changing, and the independent would be what you observe. So independent would be the substance you present to the ants, as well as the time when you did the observation, and the observation (dependent) would be ... what? Count of ants around substance? How? I can imagine that taking a snapshot of the scene and counting dots around every container would work. The hypothesis is that ants like certain kinds of food more than others, and that they like these more than plain water. The null hypothesis would be that there is no difference between any of the substances. Note that if water were the "control" then your containers should have in them watery solutions of the different substances you are testing. That is, your groups would be water with sucrose, water with starch, water with meat stock, water with nothing added. To calculate any sort of valid statistical observation you would probably have to do a number of separate observations (say a picture every 15 mins). Make sure that there are not too many unknown confusing variables or sources of error in measurement (e.g. different lighting, temperatures, distances/accessibility, consistency of food). Randomising the distribution of the containers has been noted in the previous discussion. The comparison would then be between each food and every other food, as pairs, at every specific time. Your table could consist of foodstuff in columns, and time in rows, with percentage of ants in the table cells.

           Water    Chicken    Sucrose     Starch     Total
           n(%)     n(%)       n(%)        n(%)        n
 Time  
15 min     2(4)     23(46)     22(44)      3(6)        50

30 min     7(6.7)   48(45.3)   30(28.3)    21(19.8)   106
etc

A bar graph that has "substance" on the one axis and "average percentage of total number of of ants seen at all foods together" on the other would work.

   100 |
%      |
of     |
ants   |     o
       |     o       x
       |     o       x      #
       |     o       x      #       &
     0 |________________________________
          Sucrose  Stock  Starch  Water

So would a graph showing "time" on one axis, "percent of ants" on the other, and lines of different colour for each substance (like StuRat's drawing, with times on the x-axis and percentage ants on the y). Who knows, maybe the ants go for a three course meal (chicken soup for starters at 1 hour, potatoes for main course at 2 hours and sucrose for dessert at 3 hours?), which you would see on the time / numbers graph, but not on the bar graph.

  ^                                   @ Potato
50|                                   # Chicken
  No                                  x Sucrose
  of                #                 o Water
 ants            #     #  x  x  x
  |           #           #  
  |        #           x
  |     #  x        x  @  @  #  o
  |  #  @     x  x  @        @  @
  |  x  x  @  @  @  o  o     o  #
  |  o  o  o  o  o        o
 0|________________________________>
              Time (mins)

Given a series of observations, you may apply simple statistics to calculate standard deviations and p-values (for your null hypothesis). These may be illustrated more clearly in a bar graph. Note that you cannot differentiate between sweets / carbohydrates / proteins as simply as you state - it would be prudent to specify "glucose" solution, "sucrose" solution, "starch" solution, "chicken stock", etc, and to make conclusions simply about the specifics you tested for. What kind of sugar or protein is preferred may make for another experiment. All in all, it is not as simple a project as it initially seems. Seejyb 02:04, 19 November 2006 (UTC)

Please note that, given the way ants scout and forage and "advertize" food sources by communicating through pheromone trails (see the Ant article), they will typically on any given day feast in large numbers on at most one of the food sources offered, and there may be a good deal of chance involved in which out of several suitable sources comes out as the winner. At the very least, you should each day randomize the placement of the various food dishes or containers. --Lambiam ^Talk 13:33, 19 November 2006 (UTC)

[edit] Gemstones

Can all minerals be gemstones. Explain. Thanks.

with a few exceptions - yes -pretty much so - even the lowliest piece of ground dirt if properly cut and polished can become a gemstone. Common minerals such as granite or feldspar can look nice. However some minerals are just too soft to be cut a polished - eg talc, clay, possibly mica and rock salt. Sedementary rocks present a problem becauce they are friable - however if you must mount for instance sandstone - it could be cut to shape and then coated in clear resin or varnish to give it a hard flat surface. A gemstone is just a stone that has be prepared for jewelry type use.. —Preceding unsigned comment added by 87.102.12.158 (talk • contribs)

[edit] Colo(u)r codes in molecular images

In images of (organic) molecules there seem to be customary to use certain colors for different kinds of atoms, for example carbon in black, sulfur in yellow and nitrogen in blue. How come they got these colors? I mean, the colors of carbon, sulphur or chlorine atoms may be reasonable from the elements' physical properties, but I've always wondered why nitrogen is considered to be blue, oxygen red (fire?) or phosphorous purple. \Mike (z) 19:37, 18 November 2006 (UTC)

I have some guesses: oxygen, I think, has become red because of its association with oxygenated hemoglobin, and elemental nitrogen emits blues light when it ionizes (ever wonder why our 80% nitrogen sky is blue, but only in the daytime?). Hope that helps. – Clockwork Soul 19:42, 18 November 2006 (UTC)

There's no standard - sometimes hydrogen is red and oxygen white. As for nitrogen - "why not?" seems the most polite answer - don't expect any consistent reasoning for representational colours..

Plus after red, white and black for C, O and H whats left for N- blue or green would be common choices - it's like lego.

So what you're saying is: it's purely a coincidence that in most (virtually all) images I've seen on en:wp the system of oxygen <-> red, nitrogen <-> blue, hydrogen <-> white (or light gray) - identical to what I've been accustomed to from school - is used? And ok, I didn't know there are different conventions for oxygen/hydrogen, so if there are other atoms which by different authors/image makers get different colors, I'm happy that there (usually) are text descriptions of the molecules shown in the articles, so that any wp reader used to another color convention than is used here won't get confused by two too similar depictions as of e.g. thioesters versus thionoesters (only difference according to the wp article is that oxygen and sulfur switch places). \Mike (z) 22:47, 18 November 2006 (UTC)

Edit: While writing, I did a quick check on commons and saw there a number of instances where the creator used a blueish green for carbon - those creators doing so whom I did check seemed to come from Germany or the Netherlands, so there is perhaps different customs in different countries. But ok, it seems as nobody will be able to point me to the article describing the "history of images depicting molecules" :)

[3] - added the link.

Obviously most people including me copy what they've seen - but as far as I know there is no standard laid down - just too many elements. And definately no-one would infer the structure of a compound from a picture alone - say in terms of labelling a bottle - uncertainties like this could have disastrous results (and thats not even taking into account the colour blind).CH3C(S)OCH3 and CH3C(O)SCH3 would be the simplest way to distinguish the two isomers you mention - never just a colour picture on it's own. (Sorry to waffle on)

Well the images I'm pretty sure are based on the plastic snap together kits that I'm sure you've seen - as I remember it was purely up to the user as to decide what colour represented what atom - maybe an excess of black bits led to the black is carbon convention - sorry I can't be of more help. If you really want an answer I suggest you go to the nearest university chemistry department as ask if you can speak to the oldest lecturer there - they might be long enough in the tooth to remember.

Note - these http://www.indigo.com/models/gphmodel/organic-chemistry-model-set-62053.html as an example picked at random from google surely predate the computer images. I think I've see old examples made from painted wooden balls and bits of pipe..

Well, there has been both the plastic sets, usually as on that site you hinted about, where the black ones always had four holes, the white and light green one, the red and yellows two (if I remember correctly) and so on; and images (hand drawn and computer drawn) in my old books back from school. But of course, it may be a fruitless search and I was merely curious, partly to how it comes that the colors used here in the wp articles are sort of taken for granted and used without much explanation other than assuming the reader immediately will understand that e.g. black=carbon. But now I won't nag more about it :) \Mike (z) 23:13, 18 November 2006 (UTC)

The answer is lost in the mists of time but I'm sure your original explanation was basically right - black for carbon because graphites black etc.

For the record here are balloon molecules http://www.balloonmolecules.com/Html/Galerie.htm some molecular molecules from 1875 (the oldest - probably not) http://www.chem.yale.edu/~chem125/125/history/vanthoff/tetrahedra.html

Actually there is a standard, a really old one too. August Wilhelm von Hofmann used it for his discourse On the Combining Power of Atoms when he used a croquet ball anology to explain molecules and atoms in 1865. - Dammit 23:37, 18 November 2006 (UTC)

Ah, so there was someone creating it after all! Thanks a lot Dammit, I love it when things make sense in the world :) (Coincidences usually does not, I'm afraid :P \Mike (z) 23:52, 18 November 2006 (UTC)

Yes thanks from me too, Mr dammit.

Marginally related: Cylinders of compressed gas are painted in semi-standard colors representing their contents. Modern safetly standards suggest against using the bottle color to identify the contents. ike9898 02:33, 20 November 2006 (UTC)

[edit] Safety question

Is it safe to grind saltpetre (potassium nitrate) in a coffee grinder?

on its own - yes.

Though I should say, that if you don't know the answer to that question you shouldn't be working/messing about with it.

You should fill in a Risk Assessment form before proceeeding and take suitable precuations to minimise the risk of damage to health (both yours and other peoples) 8-)--Light current 20:26, 18 November 2006 (UTC)

Don't forget to read potassium nitrate and this link from that article gives a chemical substance safety description http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc01/icsc0184.htm

Not so safe if the next person grinds coffee in the same grinder! And be very careful not to combine your finely ground saltpeter with finely ground anything else. Edison 22:00, 18 November 2006 (UTC)

Well exactly! That should be covered in the Risk assessment! (harm to others) 8-)--Light current 22:04, 18 November 2006 (UTC)

So what's the problem with a little potassium nitrate if it is safe enough to be put in food and toothpaste? --71.244.101.6 16:50, 19 November 2006 (UTC)

If you grind it in a coffee grinder, you're using much larger quantities than the ones in toothpaste or food. That's what makes it dangerous. - Mgm|^(talk) 12:46, 20 November 2006 (UTC)

Yeah but is it safe to inhale? TITQ. Also fine grinding can make explosive powders. You ought to put that on the form. 8-)--Light current 02:42, 20 November 2006 (UTC)

Be careful. Don't assumed Potassium nitrate is safe to eat. Wash the grinder thoroughly before using if you intend to put coffee beans in it.

[edit] Anabolic Steroids

I was wondering why when people use steroids, they stack them and not just use one thing? I thought just the steroid will raise testosterone levels, why isnt it all you need? thanks

Anabolic steroids lower rather than raise testosterone levels unless testosterone is the anabolic steroid being taken. alteripse 01:50, 19 November 2006 (UTC)

Yes, you stop making your own testosterone. Steroid stack and steroid cycle are not described at length in WP, but the US National Institute on Drug Abuse has a report on anabolic steroid abuse which discusses these. While I do not agree with some of the inferences, the point is well made that there is no scientific evidence for efficacy of the various stack/cycle regimes. That is, the theories for the benefit of using specific combinations have not been proven to be true at all, and such use is no less dangerous than other "therapies". Athletes follow the regimes because they accept that they work, without proof. On the other hand, there is evidence that personality changes, aggression and violence may be caused by the doses used in "stacking", as well as, of course, the well-known problems of shrinking of the testicles, impotence and infertility. Seejyb 02:42, 19 November 2006 (UTC)

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