Science desk
< January 16	<< Dec \| January \| Feb >>	January 18 >

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 17

Suffocation

Why did humans evolve to feel pain from abnormally high CO₂ levels, rather than abnormally low O₂? Unlike the former, the latter would allow people to avoid going into areas with high N₂ and little or no O₂ (nitrogen asphyxiation) --75.15.161.185 (talk) 02:55, 17 January 2011 (UTC)[reply]

How often did early humans found themselves in such conditions throughout their evolution? Dauto (talk) 03:33, 17 January 2011 (UTC)[reply]

You might find the articles on Carotid body and hypoxia interesting. I think the answer is that we didn't really evolve a mechanism to detect low Oxygen levels, but CO₂ is actually toxic, so it was much easier to evolve a mechanism to detect high levels of it. Keep in mind that it is incorrect to assume that EVERY single trait or mechanism is evolved for fitness. There are a lot of traits or mechanisms which are evolved sympathetically or inversely due to another trait which is evolved for fitness. For a very basic example, why aren't antelope legs thicker and stronger and less prone to breakage? Because longer and leaner legs are better at running. In the same way, why did we evolve that CO2 will kill us in the first place? Obviously, we didn't, it's just the result of us evolving to breathe oxygen. Vespine (talk) 03:54, 17 January 2011 (UTC)[reply]

And where on earth do you naturally get an extra high nitrogen level? The only likely place with low oxygen is high altitudes, which are usually very cold too, so no extra protective measures are needed. Graeme Bartlett (talk) 04:03, 17 January 2011 (UTC)[reply]

In electronics compartments near anything highly flammable. Many people have died when they go into a compartment to repair electronics without first venting the N₂ and adding O₂. --75.15.161.185 (talk) 04:08, 17 January 2011 (UTC)[reply]

I suspect that Graeme meant naturally occurring places. Sure, modern humans can create unusual atmospheres, but in order for low oxygen levels to have been an important evolutionary pressure for our species, our ancestors would have had to encounter low oxygen levels with some reasonable frequency. However, the presence of low oxygen levels (without also having high CO2 levels) would seem to be a very rare condition in the natural environment, and hence not something that humans would be expected to have evolved a response to. Dragons flight (talk) 04:13, 17 January 2011 (UTC)[reply]

It should be noted that large amounts of carbon dioxide actually form carbonic acid when dissolved in water; thus the carbon dioxide literally tends to create acidosis of the blood. This is a very large perturbation of body chemistry, and the body's response to it really is not all that impressive. To consider how much further evolution could go with such things, consider that mosquitoes are able to smell carbon dioxide and follow it for about 100 feet to their victims - despite, of course, producing it themselves! Wnt (talk) 08:47, 17 January 2011 (UTC)[reply]

according to our articles both Carotid bodies and aortic bodies primarily detect O2, not pH or CO2. So the answer is we already do detect it. Rmhermen (talk) 16:47, 17 January 2011 (UTC)[reply]

Tropic response to atmospheric nitrogen?

As a rule – or at least as a rule of thumb – we mammals are utter crap at evolving new signalling and sensing pathways because we just don't run through generations fast enough. We can tinker with existing pathways and mechanisms, but developing 'new' sensors is improbable virtually to the point of impossibility. So is there anything in our biological heritage that includes a tropic response to nitrogen gas? Even more broadly, are there any organisms known which respond actively to concentrations of nitrogen? (I don't count dying/not dying a a 'response' here.) Motile microbes which will move up or down a nitrogen concentration gradient, for instance? TenOfAllTrades(talk) 15:31, 17 January 2011 (UTC)[reply]

It seems unlikely, given that nitrogen makes up the bulk of the atmosphere. It's hard to do a definitive search, though, because sensors for fixed nitrogen are very common, and I can't think of a way to set up a search that filters them out reliably. (The bacterial systems that fix nitrogen could be thought of as nitrogen gas sensors, but I expect that they always operate at saturation under normal conditions.) Looie496 (talk) 18:32, 17 January 2011 (UTC)[reply]

Evolution often finds solutions that are merely "good enough". Detecting lack of oxygen rather than excess CO2 would be better, but it would be very rare that it would actually make a difference to reproductive success. Also, you wouldn't want to lose the ability to detect excess CO2 because there are situations where you get a CO2 build up without a significant drop of oxygen levels (too many people in an enclosed place, dissolved CO2 in a lake suddenly coming out of solution (see Limnic eruption), etc.). That means you would need both abilities, which is a drain on resources. Being able to detect a lack of oxygen may not be worth the cost. --Tango (talk) 19:26, 17 January 2011 (UTC)[reply]

I think that bats, bloodhounds, and star-nosed moles would each disagree with you in their own special way. While it seems like some mammals are "terminally differentiated", reproducing too slowly to evolve quickly or even to prevent losses of useful little things like vitamin C from the genome, we yet see that some of the longest-lived mammals somehow evolved rapidly in form and function to become humans, which was one of evolution's more curious accomplishments. And of course there remains a vast pool of various little shrewlike things that outnumber all the rest of us, just waiting to start down some new evolutionary path and claim a new place in the limelight. (Oh, and note the comment about O2 and the carotid body above) Wnt (talk) 22:03, 17 January 2011 (UTC)[reply]

Detecting N₂ directly would be very difficult/impossible because it is non-polar which means it is difficult for any other molecules to grab hold of, after all, this is why there is so much of it in the atmosphere, because it doesn't react with anything. For species that fix nitrogen using nitrogenase, there is no need to have a tropism to it because N₂ is everywhere. SmartSE (talk) 00:49, 18 January 2011 (UTC)[reply]

Well, as I wrote above, your own answer explains how it could be done: to build a biological N₂ detector, all you would have to do is couple nitrogenase to a detector for fixed nitrogen, of which there are many examples. But as you also say, such a thing would be useless, because N₂ is everywhere. Looie496 (talk) 22:07, 18 January 2011 (UTC)[reply]

Future space journeys

in future the man will find better ways for solve weightloss problem in space jurnays . i forcast that this mystry is hidden in comets and sattlite and space craft groups will have diffrent missions . we will find severel mystrys of planets and moons with particle sending method that i want to publish . i have good ideas for this. a. mohammadzade — Preceding unsigned comment added by A.mohammadzade (talk • contribs) 05:02, 17 January 2011 (UTC)[reply]

Hello, I'm guessing English isn't your first language so apologies if there is a question there which I'm not seeing. The reference desk is for people who seek referenced answers to specific questions relating to science. Do you have a question? Vespine (talk) 05:43, 17 January 2011 (UTC)[reply]

The artificial gravity article may be of interest to you. 71.198.176.22 (talk) 06:32, 18 January 2011 (UTC)[reply]

that is so ,my mother toungh is turkish ,so i have some difficultys in english . I have write my special questions about solar system last jan 11 under the subject "any one with new ideas for creation theories of solar system "wich shows my new theory upgrading from new explanation of objects and planets belts and astroids in solar system . I wrote them not to find replays but for showing nessesity for development and changing in thus theories A.mohammadzade jan 18 iran—Preceding unsigned comment added by 78.38.28.3 (talk) 04:03, 18 January 2011

Electromagnet.

Define Electromagnet.Chetan the Champ (talk) 10:29, 17 January 2011 (UTC)[reply]

Do you need a dictionary? Here: Electromagnet. Or is this a homework question? Ariel. (talk) 11:03, 17 January 2011 (UTC)[reply]

Bread

What are the health problems from eating stale whole wheat or seed bread? If there is no mold on it and it was in the fridge? --41.213.125.249 (talk) 10:40, 17 January 2011 (UTC)[reply]

Why should there be health problems? Even if there was mold on it it would probably be harmless (most, but not all, molds are harmless when eaten (as opposed to inhaled)). What do you mean by "seed bread" - all bread is made from seeds. Ariel. (talk) 11:00, 17 January 2011 (UTC)[reply]

The term probably refers to Whole grain bread. It may also refer to Seed cake. Not sure which the OP means. Regarding health effects, presuming that there isn't any alergic concerns (i.e. you wouldn't have negative health effects from eating it fresh) and it isn't rotten or spoiled (as the OP says, no mold) then stale bread is just "dried out", i.e. slightly less water than fresh bread. I would say that such bread is perfectly safe, again with the caveats that there is no spoilage and there is no allergy concerns. --Jayron32 13:59, 17 January 2011 (UTC)[reply]

I regularly eat soda-bread which contains sunflower seeds, linseeds and sesame seeds. Maybe something like this is what the OP is referring to. I agree that there are few health risks in eating stale bread, with or without seeds. Our stale bread (not the soda bread) is made into breadcrumbs for use in other dishes. I'm still here! Oops, sorry that's WP:OR. Richard Avery (talk) 14:16, 17 January 2011 (UTC)[reply]

Stale white bread should be made into bread and butter pudding. DuncanHill (talk) 16:16, 17 January 2011 (UTC)[reply]

Rye bread and other breads infected by fungus could historically result in Ergotism. ~A H 1^(TCU) 01:23, 18 January 2011 (UTC)[reply]

gastric acid

do all other animals use HCl in their stomach as we do? — Preceding unsigned comment added by Sina-chemo (talk • contribs) 11:09, 17 January 2011 (UTC)[reply]

Yes, it does seem so (although I can't say with 100% certainty). Chlorine is very common in the environment - from ordinary salt, so it gets used as the acid plus when it's time to neutralize the acid it makes ordinary salt, and salt is used for other things as well (sodium is the main driver in nerves). However not all animals have stomach acid, acid breakdown is not the only form of digestion. Ariel. (talk) 11:52, 17 January 2011 (UTC)[reply]

No: In most insects, midgut pH is either mildly acidic or neutral. Lepidopteran and trichopteran larvae, scarabaeid beetles, and nematoceran flies have alkaline midguts, .... --Sean 15:27, 17 January 2011 (UTC)[reply]

Your reference to the midgut confuses the issue -- humans also have basic midguts. HCl is secreted in the stomach, but bicarbonate is secreted from the pancreas, and a look at our midgut and foregut articles seems to establish the change of foregut to midgut at the point of fusion with the bile duct -- looking at the bile duct article reveals that this duct meets with the pancreatic duct and enters the duodenum at the ampulla of Vater. Thus, insects are hardly unique in having basic midguts -- I'd say humans and most mammals do to. DRosenbach ^{(Talk | Contribs)} 19:17, 17 January 2011 (UTC)[reply]

Vikrell wha

whats Vikrell — Preceding unsigned comment added by Tommy35750 (talk • contribs) 17:19, 17 January 2011 (UTC)[reply]

Resin & filler. --Sean 17:47, 17 January 2011 (UTC)[reply]

e/c Any context? Can't find anything about it on Wikipedia, but it appears to be a product name by the Sterling (Kohler) plumbing company for a range of bathroom and kitchen products: see [1]. --jjron (talk) 17:48, 17 January 2011 (UTC)[reply]

" Vikrell is a solid composite material made of resins, fiberglass and filler that is exclusive to Kohler Company." [2] (See "shower stalls FAQs" box at bottom right of page). It apparently has integral pigment rather than a paint-like top layer, hence chips don't show. 81.131.68.227 (talk) 17:52, 17 January 2011 (UTC)[reply]

It's a brand name for a Solid surface countertop material. Ariel. (talk) 20:32, 17 January 2011 (UTC)[reply]

Gaseous compounds without gaseous elements

Are there any chemical compounds which are gaseous at STP, despite containing no chemical element which is gaseous at STP? --84.61.155.161 (talk) 17:37, 17 January 2011 (UTC)[reply]

Not that I can think of, but carbon disulfide (b.p. 46.3 °C, 115 °F) comes pretty close. Physchim62 (talk) 19:07, 17 January 2011 (UTC)[reply]

Methyl bromide only works when you consider methanol an "element" (which it isn't), or phosphorus tribromide which only produces gaseous fumes during hydrolysis. Possibly sulfur dibromide? ~A H 1^(TCU) 01:20, 18 January 2011 (UTC)[reply]

Sulfur dibromide doesn't exist at STP. The next nearest I can find is boron tribromide (b.p. 91.3 °C, 196 °F). Physchim62 (talk) 12:19, 18 January 2011 (UTC)[reply]

Citric acid in fruit

My family has been kicking around a recipe for corn cob jelly, and our most recent attempt at making it was somewhat of a flop. According to the package, pectin requires acid to work, and the typical way of doing this is to add lemon juice. The problem is that corn cobs don't make for a very strong flavor and the end product was rather more lemon-tasting than I'd like. Other than laboratory supply of citric acid (or hydrochloric for that matter!) is there a source of food-grade acid that isn't quite as strong a flavor as lemon juice? I was thinking vinegar, but that's unlikely to work well with a sweet product like a jelly. SDY (talk) 20:16, 17 January 2011 (UTC)[reply]

I don't know where you live but in NZ you can buy citric acid and tartaric acid in most supermarkets. However from my experience in making paneer, citric acid still imparts a fairly strong taste. Haven't though of trying tartaric acid for some reason. You could try various acidic fruits I guess. Pineapple or green kiwifruit perhaps? Perhaps even lime will be a taste you find okay. While looking in to tartaric acid for making paneer I found this [3] where they also tried lactic acid and ascorbic acid (you'll want to be careful you don't overdose on vitamin C I guess). Finally you may want to do a few tests, perhaps you're using way more lemon juice then you need? Nil Einne (talk)

C is water soluble and it's very hard to get an overdose. A and D and the other fat-solubles are the problems for overdose. I'll have to look at a different grocery store. Safeway (US, Washington state) doesn't carry citric and tartaric from what I've seen, though I guess I've never asked. SDY (talk) 20:46, 17 January 2011 (UTC)[reply]

The vitamin C article says it exhibits remarkably low toxicity, the LD50 for an average person would be over 800 grams, and "The mechanism of death ... may be more mechanical than chemical". :) 81.131.16.71 (talk) 20:58, 17 January 2011 (UTC)[reply]

Okay no concerns for ascorbic acid then so that's one possibility. I should clarify the citric acid and tartaric acid I'm thinking of is normally available in crystalline form, see [4].

This result from a search for 'where to buy citric acid' may be helpful [5] (the purpose there may not be food related but most of the suggestions sound like they will be fine). In particular a brewing shop may be something to look in to. I know someone who makes their own energy gels and citric acid is used, so perhaps a health food or sports/exercise supplement shop will also have something (although they may just want to sell you premade stuff). [6] (UK apparently) suggests a home brewing shop as well hence my recommendation.

P.S. Reading the forum suggestions a little more closely, it also sounds like you may not want to (try to) purchase too large quantities...

Nil Einne (talk) 21:50, 17 January 2011 (UTC)[reply]

Cheese-making supply shops sell citric acid. --Sean —Preceding unsigned comment added by 208.54.44.51 (talk) 00:25, 18 January 2011 (UTC)[reply]

Flash flood tanks

Can a flash flood carry and destroy an army tank? --109.78.87.34 (talk) 21:26, 17 January 2011 (UTC)[reply]

I don't see why it couldn't carry one away. Flash floods can remove houses from their foundations, and in terms of absolute weight, a house is heavier than a tank. "Destroy" may be a harsh word, but I could see a tank being lifted off its treads and moved by such a flood. --Jayron32 21:34, 17 January 2011 (UTC)[reply]

From M4 Sherman: 66,800 pounds / (5.84 m * 2.62 m * 2.74 m) = .723 g/cm³ leading to the surprising result that tanks float. Of course that assumes that it's a cube, which it isn't. It's probably denser than that, but it's still reasonably close to the density of water, so water will have no trouble carrying it. Houses float too BTW, that's the main reason flash floods can move them. Ariel. (talk) 21:57, 17 January 2011 (UTC)[reply]

I don't believe so, or at least not to a catastrophic degree. Many modern main battle tanks are capable of deep wading, which means they can drive through water that's as deep as they are tall (with the help of a snorkel) - see File:Zwei_Leopard_2A5_beim_durchqueren_eines_Gewässer.ogg where two modern Leopard 2 MBTs ford a river, with only their snorkels and the ends of their gun barrels above water. They can only achieve this if they're heavier than the water they displace (that is, that they don't float). It seems other MBTs, including the T90 and the Abrams M1 can deep wade too. So that demonstrates that, fully immersed in water, they have enough net downforce to allow the treads to engage enough to drive the vehicle through the river at some speed (which shows they're not just on the ground, they're still quite firmly on the ground). There have been fully amphibious ("swimming", which means floating) tanks, like WW2's Swimming Sherman, but those either needed an inflatable float (see DD tank#Sherman DD) or to be specifically designed to float (like the lighter Expeditionary Fighting Vehicle). Now whether the driver of a wading tank fancies the idea of driving it around in what has become essentially a murky, obstacle-filled, fast-flowing river is another matter. The wading capability is designed either for hot landings on beaches from landing craft, or for fording rivers, so they're not designed to be terribly effective at doing anything but going in a straight line in water, and not for very long. -- Finlay McWalter ☻ Talk 22:23, 17 January 2011 (UTC)[reply]

Maybe it's the difference between loaded weight and unloaded. Probably the number given in the article is for unloaded. Also a tank is not a cube, so the simplistic volume calculation is certainly too large. I was just going for an order of magnitude calculation. Ariel. (talk) 22:54, 17 January 2011 (UTC)[reply]

There's not much difference, that I can figure, between the loaded and unloaded weight. Looking at the Leopard 2, I reckon its ammo (43 rounds at 25 kg/round) weighs 1075kg, the fuel (1160 litres of diesel at around 0.84 kg/litre) weighs 975kg, and if three of the four crew swim for it (say 3 x 100kg) that's 2.3 tonnes. That sounds like a lot (it's more than two cars) but when you consider the full Leopard 2 weighs in at a jaw-dropping 62 tonnes, the laden/unladen differential is only 4% or so. -- Finlay McWalter ☻ Talk 23:17, 17 January 2011 (UTC)[reply]

It seems that a "flash flood" can mean anything from an accumulation of rainwater at low points of streets where the water is essentially standing still, to a vertical wall of water roaring through a canyon downstream of a failed dam. A tank should have decent chances of operating in the former, but has essentially no possibility of surviving the latter.

As soon as the flooding water is flowing, lateral forces on an obstacle become at least as important as byoyancy. –Henning Makholm (talk) 22:56, 17 January 2011 (UTC)[reply]

For an extreme example, the Johnstown Flood picked up and moved entire locomotives; I am pretty sure such locomotives compare favorably in terms of density and weight to a tank. --Jayron32 00:11, 18 January 2011 (UTC)[reply]

And floods aren't just water moving, either. There's stuff being carried in that water. Boulders. --jpgordon^{::==( o )} 07:21, 20 January 2011 (UTC)[reply]

I have seen footage of flash floods higher then a two story house. --109.78.140.181 (talk) 21:37, 20 January 2011 (UTC)[reply]