Wikipedia:Reference desk/Archives/Science/2012 June 11

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June 11

testosterone

Questions and responses removed because we cannot provide medical advice as a matter of policy. Please consult a qualified medical professional; best of luck. Anonymous.translator (talk) 02:16, 11 June 2012 (UTC)

paranormal effects of Ghungroo anklet

Context: in my editing during Ghungroo in the wikipedia encyclopaedia, the editing reached in a question and to get answer i had added my e-mail id; which resulted in automated warning. then i learnt, said question can be asked here also. thus i type entire "edited portion" by me, here, for further help: If some one can clarify, this point is written. In the web page: www.travelblog.org/Asia/blog-455847.html, the following can be read: “We had a camp fire inside, in the verandah. We were able to hear the insects noise loud. It appeared as if somebody with ghungroo was walking just beside the window mesh and Doppler's effect was also there (The Ghungroo sound used to get loud and again disappear as if somebody is running towards the window and again going far.) If we had heard the ghungroo aawaz inside the bungalow don't know what we would have done? The sound still murmurs in my ears. I do not know who or which animal was roaming around with ghungroo and whom it was trying to romance among the three?? :):)”. Even outside the forest, such sound is heard by the person editing it, in residential colonies. In his enquiries, there are no animals, birds or insects which create such sound. It is told that, female ghosts, a particular classification in Kerala “Rakhta/ blood Yakshi” do create this sound. Can some one clarify this phenomena ? This sound is heard not by every one, but only a few selected ones in the group, at that particular sound. for reply's sake e mail is added, eventhough no need while editing wikipedia: <email redacted> — Preceding unsigned comment added by Ramanathan2108 (talk • contribs) 09:35, 11 June 2012 (UTC)

It's not that an email address is unnecessary, it's that it's not permitted. As it says at the top of the page: Do not provide your contact information. E-mail or home addresses, or telephone numbers, will be removed. You must return to this page to get your answer. Karenjc 12:06, 11 June 2012 (UTC)

A Ghungroo is a musical anklet tied to the feet of classical Indian dancers. DriveByWire (talk) 13:27, 11 June 2012 (UTC)

There is no such thing as a ghost. Look for the rational explanation. 217.158.236.14 (talk) 13:33, 11 June 2012 (UTC)

A Ghungroo in Bollywood. (video) DriveByWire (talk) 14:50, 11 June 2012 (UTC)

Boiling point for Phosphorus

The WP article on Phosphorus, http://en.wikipedia.org/wiki/Phosphorus, gives the boiling point (presumably for standard pressure, 1.01325 Bar) as 280.5 C (553.7 K). This ought to be for the standard state, P₂, to be consistent with WP articles on other elements. However, the NIST-JANUF tables (4th Ed) give the standard state as P₁ and the boiling point as 1180 K at 1 Bar. The Ihsan-Barin tables (2nd Ed 1993) give the standard state as P₂ and the boiling point as 1180 K at 1.01325 Bar. Googling "boiling point phosporus" returns sites similarly disaggreeing. It is of course quite unlikley that P₁ would have the same boiling point as P₂, and unlikely that P₁ would boil higher than P₂. What is the most common standard state? What is the correct boiling point for P₁ and P₂? It would be nice if the WP articles gave the allotrope/catenate for which the triple, melting, boiling, and critical points are quoted - it would save some confusion. Which one of the two standard pressures (1 Bar as per IUPAC, 1 ATP as per USA) the data is applicable to would be good too. Keit120.145.195.11 (talk) 10:17, 11 June 2012 (UTC)

That is because the standard state is P₄. Plasmic Physics (talk) 10:39, 11 June 2012 (UTC)

Gee, Plasmic, you've just made things more difficult. Do you have any references for P₄ being the standard state, noting that NIST-JANUF bible gives (on page 1817) the standard state as P₁? The What are the temperature points for P₄? I thought that phosphorus in the gas state can only be P₁ or P₂. Therefore the standard state in the gas phase at least must be P₁ or P₂. If that is so, and the minimum energy state when liquid is P₄, then shouldn't there be a different temperature for boiling and for condensation? I haven't come across two temperatures, as in one listed for boiling, one for condensation. Keit120.145.195.11 (talk) 11:09, 11 June 2012 (UTC)

Sorry, I don't have the data on hand. I just did some reading of the article myself, apparently the allotropy of phophorus is a messy business, much like sulfur. It changes from one crystallomorph to another as the solid heats up, while at the same time starting to decompose into different molecular structures. The diatomic and monoatomic molecules tend to exist only in the gas phase, mixed with other molecular varients. Plasmic Physics (talk) 23:23, 11 June 2012 (UTC)

If you want some insight, try octasulfur. Plasmic Physics (talk) 23:54, 11 June 2012 (UTC)

Does anyone know which more kinetically stable: a phosphorus icosaherdron, or a phosphorus tetrahedron? Plasmic Physics (talk) 23:54, 11 June 2012 (UTC)

Does anyone know (from a reliable reference, or from logical process) the boiling points for P₁ and/or P₂? Keit58.170.163.132 (talk) 01:06, 12 June 2012 (UTC)

From the same phosphorus article, I can tell you that it is next to impossible to experimentally find the boiling and melting points. They are just way too reactive, they polymerise faster than what they condense at. If you're lucky, you can maybe find theoretical calculated values. Plasmic Physics (talk) 01:20, 12 June 2012 (UTC)

Since all references I can find give the boiling point as either 554 K or 1180 K, theoretical values will do nicely, as even if not accurate, they would identify which of these two values is wrong, and which value should be used in other calculations. If only I knew where to look. Keit124.182.173.247 (talk) 01:42, 12 June 2012 (UTC)

ChemSpider gives 741.33 K, 769.65 K, and 796.85 K for P, P₂, and P₄ respectively, as their boiling points. (According to the EPIsuite predictions.) Plasmic Physics (talk) 02:47, 12 June 2012 (UTC)

P₄ thermolyses into P₂ at ~1180 K, P₂, thermolyses above an even higher temperature. Plasmic Physics (talk) 02:53, 12 June 2012 (UTC)

ChemSpider gives 435.17 K, 450.94 K, and 480.72 K for P, P₂, and P₄ respectively, as their melting points. (According to the EPIsuite predictions.)

I was in the university library today, and had a look at a few references. The OP is correct in stating that the NIST-JANUF tables (4th Ed) on page 1817 gives the reference state at all temperatures as P₁, and it gives the boiling point as 1180.008 K at 1 bar. Further, the Phsophorus data has been repeated unchanged (except for a minor fidle to change from 1 ATM to 1 Bar) in each edition since 1961. So an error is unlikely, it would have been corrected by now. Also, the 1180 K boiling point is supported by P's position in the Periodic Table, 554 K would be unlikely. I also looked in Thermodynamic Properties of The Elements, published by the American Chemical Society. It gives the standard state as red phosphorus solid up to 704 K, the sublimation point, and P2 gas above. Note that http://en.wikipedia.org/wiki/Phosphorus says red phosphorus sublimes at approx 416 C ie 689 K. I can't say why Plasmic Physics thinks the standard state is P4, however one might expect the standard state to be the lowest energy state, and you do find different authors choose different standard states. I assume that WolframAlpha, which gives the boiling point as 553.7 K is in error, and this error has been copied into the Wikipedia article. I found ChemSpider to be hopelessly inaccurate. Try looking up the boiling points for O₂ for example. Ratbone58.170.167.209 (talk) 12:46, 12 June 2012 (UTC)

The reason P₄ is standard is because that is the most common molecule in the gas when white phosphorous boils or red phosphorous sublimes. You are going to get a similar issue with sulfur and the S₈ molecule. The gas contains S₄ also and at higher temperatures S₃ and S₂ and only at extreme temperatures will you find significant S₁. There is no point insisting on P₁ as you will not find it around at transitions between liquid and gaseous phosphorous. Graeme Bartlett (talk) 12:57, 12 June 2012 (UTC)

Further to my post above, perhaps in a sense Wolfram Alpha is not in error - the ACS publication gives the boiling point of white phosphorus (not a standard state) as 554 K, exactly as Wikepedia does. Regarding Graeme's view, it's not me that is doing the insisting, it's NIST (USA standards body) insiting on P₁, and the American Chem Society insisting on P₂. Regarding sulphur, NIST-JANUF 4th Ed gives the standard state as a mixture of S₁ and S₂ with traces of other forms. See page 1859. With carbon, NIST-JANUF give the standard state as graphite up to submlimation (~3900 K), then the monatomic form. But the most dominant form in gas appears to be C₃. If heated, C₃ splits into more and more C₂ and C₁. So where something transitions, and what it transitions to, is not necessarily the key. What reference gives P₄ as the standard state for phosphorus? Ratbone58.170.167.209 (talk) 13:28, 12 June 2012 (UTC)

Acid (not the trippy kind)

I'm looking for some scientific assistance on aspects of a story I'm working on; I am doing my own research as well but I haven't done science since I was at school, and I'm struggling to find specifics in terms I can understand and work things out from. Acid; probably sulfuric or nitric.

1) If it's strong enough to burn skin through ordinary clothes (let's say ordinary outdoor clothes, so through a jacket and shirt), what effect would it have on buildings and other structures?

2) How long would it take to significantly damage the structure of an average building?

2a) Would that depend on the kind of brick/stone it was made of?

3) What would it do to a car and to road surfaces etc.?

4) What effect would extra layers of clothes have - would a drop of acid keep dissolving subsequent layers, or does it stop after a while?

5) Are there any widely available materials that are completely resistant to these acids?

6) What's it like to be burned by acid?

6a) Does it sizzle?

6b) Does it smell like burning?

Any assistance greatly appreciated :) Morgana Fiolett 15:21, 11 June 2012 (UTC)

I numbered your questions for you. StuRat (talk) 15:27, 11 June 2012 (UTC)

1) You would need a lot more acid to substantially damage the structure of a building (versus just cosmetic damage), unless you applied it specifically to critical points, like rivet heads in a steel frame building. StuRat (talk) 15:30, 11 June 2012 (UTC)

2a) Yes. Limestone is particularly subject to acid erosion, since it's alkaline and an alkaline material plus an acid react to create a salt and water. Note that Egyptian granite artifacts brought to places with acid rain, such as Cleopatra's Needle, have also been damaged because of it. StuRat (talk) 15:35, 11 June 2012 (UTC)

Cement is also very susceptible to dissolution by acid as is mortar. Destroying the mortar between the bricks will do significant damage. 203.27.72.5 (talk) 21:19, 11 June 2012 (UTC)

3) Cars would tend to rust after having the paint and protective cladding dissolved off the metal. StuRat (talk) 15:42, 11 June 2012 (UTC)

4) Acids might go right through the gaps between the threads in clothes, just like water. Battery acid (sulfuric acid) can also dissolve some clothes. StuRat (talk) 15:44, 11 June 2012 (UTC)

5) Platinum is often used in labs with strong acids, to contain them without reacting. See Reactivity series. StuRat (talk) 15:47, 11 June 2012 (UTC)

Both nitric and sulfuric acid can be contained in glass, which is much more widely available than platinum. Also many plastics do not react with those acids. 203.27.72.5 (talk) 21:23, 11 June 2012 (UTC)

6) A minor acid exposure can cause irritation, itching, and drying of the skin. A major acid burn likely feels like other types of burns, such as a thermal burn, sunburn, or radiation burn. StuRat (talk) 15:51, 11 June 2012 (UTC)

6a) With a strong enough acid, which produces a gas as product of it's reaction, yes, it would sizzle. Incidentally, you can get this same effect with a base, like 3% hydrogen peroxide, when applied to a cut.

H₂O₂ fizzing when it's applied to a cut isn't a simple acid/base reaction; the breakdown is a catalysis, performed by the enzyme catalase. Tonywalton ^Talk 17:13, 11 June 2012 (UTC)

Yes, by "this same effect", I meant "fizzing when a chemical is applied to flesh". StuRat (talk) 17:28, 11 June 2012 (UTC)

6b) No, it would smell like a chemistry lab. StuRat (talk) 15:54, 11 June 2012 (UTC)

Probably, but that really depends on what the acid's acting on. Concentrated sulphuric acid on sugar, for instance, dehydrates the sugar, leaving a solid foam of carbon and a smell of, well, caramel. Morgana, you might try researching into the activities of John George Haigh regarding dissolving flesh in concentrated sulphuric acid. Tonywalton ^Talk 17:19, 11 June 2012 (UTC)

When sulfuric acid reacts with hair it also smells just like burning hair. I found that out the hard way. 203.27.72.5 (talk) 21:23, 11 June 2012 (UTC)

Incidentally, if you're looking for a fictional substance which can dissolve through anything and not be "used up", you want a catalyst. Those cause a chemical reaction, but remain unchanged as a result of the reaction, so they are free to go on and cause more reactions. They speed up reactions which would have occurred anyway, eventually. Chlorofluorocarbons, for example, are a class of catalysts which destroys the ozone layer. Table salt is also a catalyst for the rusting of iron and steel. Perhaps your fictional "catalyst from hell" could react with atmospheric oxygen, water vapor, and carbon dioxide to create carbonic acid, or with atmospheric nitrogen to create nitric acid, using sunlight to power the reaction, and dissolve nearly everything in it's path ? StuRat (talk) 16:05, 11 June 2012 (UTC)

(1, 2, 4) In general, chemicals are consumed when they react. As an acid dissolves or burns or whatever, it becomes neutralized or more dilute, reducing its power to do...whatever. It takes a lot of a corrosive chemical to do widespread damage by corrosion (vs substantial but locallized damage, as StuRat notes).

For any acid or other chemical, there are generally many materials that are resistant to it. Concentrated sulfuric acid and nitric acid are sold commercially in glass containers. Concentrated hydrochloric acid is sold commercially for cement cleaning in glass or plastic bottles...it dissolves a bit of the cement but only "a bit" (neutralizing itself in the process). For any acid, there's something it will destroy and something else that will be inert, and sometimes you can even find complementary cases. Acid "strength" is only part of the picture, since some of the specific chemical components (not just "what makes it acid") can be separately reactive in other ways. HF is a weak acid that eats glass and even small amounts on skin are incredibly painful and possibly fatal but it does not react at all with many plastics, and other much stronger acids don't react with glass at all and small amounts on skin have no or only much less drastic effects. DMacks (talk) 15:37, 11 June 2012 (UTC)

You might go for a combination of acids; see for example Aqua regia, which will dissolve platinum. Or go completely fictional and use Alkahest. Tonywalton ^Talk 15:58, 11 June 2012 (UTC)

Re your question on the effects of a strong acid on a building, the effects are slow and undramatic, especially for a one-time event. Acid will cosmetically damage limestone, but it would take a long time to have any structural effect, and then only if it is reapplied, as the reaction with the stone has the effect of neutralizing the acid. Most other masonry material would be reasonably resistant in periods of less than a decade. Concrete would gradually become powdery and weakened, but it would take a lot of acid. Much the same thing would happen for steel: it would corrode, but for any steel element other than sheet metal that'd be about it unless it was applied over a long term, as in years. As StuRat notes, targeted application would have more effect, but riveted and bolted connections are still quite substantial and tend to be redundant. Even with sheet metal it will take a long time. I had a broken battery case in my VW Beetle in college (the battery in a Beetle is under the back seat on the floor pan): I mopped it up with baking soda, but gave up after a while when I ran out of soda. I sold the car four years later and the battery hadn't fallen out into the road yet.Acroterion (talk) 15:38, 11 June 2012 (UTC)

By the way, I replaced the battery (the victim of a friend who tried to jump-start his car from mine and cross-connected the cables, blowing out a couple of cells) and used up a box of baking soda when I changed batteries, but it was still fizzy when I ran out of soda. Acroterion (talk) 21:32, 11 June 2012 (UTC)

For question number 2, not that this should ever be tried EVER (not only for the obvious reasons but because it involves handling mercury) but for certain metals amalgamation is the surest way to "dissolve" a structural member. -RunningOnBrains^(talk) 18:09, 11 June 2012 (UTC)

What should never be tried ? Leaving a leaky battery in a car ? Where's the mercury ? StuRat (talk) 18:14, 11 June 2012 (UTC)

I was replying to the OP's question, I see that my indentation was a little ambiguous. I assumed that part of his story involved damaging a building with acid, so I offered a possible alternative material. The obvious part was not to try it on an actual building. I've edited it to make clearer what I was answering. Also, why are we whispering? :) -RunningOnBrains^(talk) 19:40, 11 June 2012 (UTC)

I fixed your indentation to show you were replying to the OP, not Acroterion.

I whisper when saying anything that's not an answer to the Q.

Now, what mercury are we talking about ? StuRat (talk) 20:01, 11 June 2012 (UTC)

Click the link... amalgamation is when you mix mercury to another metal. Really cool video here; but again, mercury is dangerous so DON'T TRY THIS AT HOME KIDS! -RunningOnBrains^(talk) 22:09, 11 June 2012 (UTC)

OK, I was not familiar with that definition of "amalgamation", but was going with the more common "any combination of two or more things". StuRat (talk) 23:27, 11 June 2012 (UTC)

I thought the definition of amalgam as a mixture of things was derived from the term for mixture of metals with Hg. And also, haven't you ever heard of a dental amalgam? Maybe I'm just biased because my family have bad teeth, but I thought they were a pretty common thing. 203.27.72.5 (talk) 02:33, 12 June 2012 (UTC)

Based on the lack of "mercury" or "hydrargyrum" in the word, I doubt that origin. Looking up the etymology, I found this ref (page 274): [1]. It states "AMALGAM is an old alchemical word, probably a perversion of the Latin malagma, a mollifying poultice, traceable to the Greek malassein, to soften. Other early writers associate it with ana, together, and gamos, marriage. Bacon (1626) writes the word 'amalagma'." So, it seems that the general meaning came first, and then the more specific application to amalgams of mercury. And yes, I've heard of dental amalgams. StuRat (talk) 21:51, 12 June 2012 (UTC)

I have a gruesome story about acid which seems relevant. My dad worked in the petrochemical industry for a while, and witnessed a fatal industrial accident. A worker was on a catwalk above a large, open vat of highly concentrated sulfuric acid. He had a full "chem suit" on. But, apparently forgetting where he was, he removed his head gear/mask to scratch an itch, accidentally inhaled, and passed out immediately from the fumes. He then fell between the bars, into the vat, and fully dissolved in a rush of bubbles. When they emptied the tank, nothing was left of him and his clothes, except his gold wedding ring. If I remember correctly, I believe this was a Union Carbide plant, near Whiting, Indiana (a suburb of Chicago). So, their lax safety practices (like even having a catwalk above an open tank of acid), might have been a warning about their later Bhopal disaster, had anyone cared to listen. StuRat (talk) 20:15, 11 June 2012 (UTC)

Nothing left except the gold ring, eh?. This is the same as an ancient movie I saw once. Give me some time and I'll remember the name of the movie or who starred in it. Bit sus, Stu. Wickwack121.221.229.129 (talk) 01:26, 12 June 2012 (UTC)

Since everyone so far has seemed to assume that the OP is only asking about a splash or a smear of acid, I will consider what would result if a bulk container of concentrated sulphuric or nitric acid ruptured in a builing. Having a large amount of acid pour into a brick room and flow out it's windows and doors would expose the brick work to a great deal of acid. If the bricks themselves do react with the acid then the acid will more or less uniformly degrade the walls it contacts in proportion to it's flow. If the bricks do not react quickly with the acid, then the effects will be worse, with the acid being consumed only in degrading the mortar and thus quickly destroying the structural integrity. Assuming a cement floor it will also react with the floor helping to neutralize the acid. It will also react mainly with the lower parts of the wall as that is where it will make most contact. This would severly weaken the structure leading to the walls probably falling inward. If the masonry is reinforced with rebar or similar this will also be attacked by the acid once it has penetrated a significant distance into the wall. Also of interest is that sulfuric acid releases a lot of heat when it makes contact with water. A few mls added to a cup of water will make it boil briefly. In a building with a water supply it could make a big mess. 203.27.72.5 (talk) 21:48, 11 June 2012 (UTC)

Its a question of scale and basic stoichiometry. The amount of material the acid will dissolve cannot exceed the amount of acid there is (as measured by the actual number of acid molecules). So, if you had, say, 1000 kg of concentrated sulfuric acid, that's 980 kg of actual sulfuric acid (conc. H2SO4 is 98% ), and since sulfuric acid has a molar mass of 98 g/mole thats 10,000 moles of sulfuric acid. Thus, if you know what you are dissolving, you can calculate the maximum mass of the substance the acid would dissolve. Say something like limestone (basically calcium carbonate.) 1,000 moles of calcium carbonate (100 g/mole) would weigh 1000 kilograms, meaning that 1 metric ton of concentrated sulfuric acid would dissolve 1 metric ton of limestone. Since bricks, concrete, and other building materials probably contain some material which may be unreactive to sulfuric acid, you would dissolve even less. So basically, to dissolve a brick and mortar building you would need a minimum of an equivalent mass of sulfuric acid, and likely a substantial amount more. Highly impractical. --Jayron32 22:16, 11 June 2012 (UTC)

You wouldn't need more acid because of parts that don't dissolve, as the acid would not be "used up" by those, but would go around them and dissolve the next bit. StuRat (talk) 22:26, 11 June 2012 (UTC)

"Since bricks, concrete, and other building materials probably contain some material which may be unreactive to sulfuric acid, you would dissolve even less." Acutally, this would cause more damage to the structure. You will always dissolve the same amount of lime (as you pointed out). If there are unreactive materials (like sand and aggregate in concrete) then they will not contribute to neutralizing the acid but once the lime around them is dissolved they will also no longer contribute to the structural integrity. Regular concrete is about 1/6 portland cement which is in turn only 2/3 lime at most (so regular concrete is about 11% lime).

It is also important to consider the kinetics in addition to the scale and stoichiometry. If the acid's bulk flow out of the door is fast enough you might only have say the equivalent of half of it actually react to near completion with the lime and metal in the structure.

If we imagine a bulky box of 1000L(1840kg) of sulphuric acid suddenly released into a square room of say 25 square meters with a closed door, the acid will make contact with the walls up to a height of 4cm. The acid will be in contact with 25 square meters of floor and 0.8 square meters of wall. If the floor is concrete it will react with the acid and neutralize it. If we assume that the proportion of reaction with the floor and walls is determined only by the surface area of contact then ~3%(57kg) of the acid is used up in reacting with the walls. For lime (molecular mass 56g/mol) only 560kg is dissolved by 1t of sulfuric acid. If the walls are made out of regular concrete, then the lime portion of 513kg of concrete will be dissolved. That's 25.7kg per meter of wall. If we take the density of concrete as 2300kg/cubic meter and assume the acid dissolves away a perfect prism extending into the foot of the wall, the hole is 27.9cm deep (though it still contains undissolved aggregate). That's more than enough to topple most concrete walls. 203.27.72.5 (talk) 23:10, 11 June 2012 (UTC)

When bricklayers have finished a wall, the wall usually looks a bit messy becausee of odd bits of dirt and mortar adhering to the sides of the bricks. They use "brick cleaner" to get this off, usually by brushing the brick cleaner on to the bricks with a small paint brush. Brick cleaner is a mild acid, HCl I think. It does not attack brick at all, but does loosen sub-millimeter thicknesses of mortar. So, if any common acid has any effect on concrete or brick, it will be too slow and feeble to have any significance re Morgana's story. Wood is somewhat resistant too. But metal window and door frames - different story. Wickwack121.221.229.129 (talk) 01:26, 12 June 2012 (UTC)

The chemistry of cement is complex, but it probably would have been more useful if I consider the lime component of cement to become slaked lime upon setting. It is also important to note that since

$Ca(OH)_{2}+H_{2}SO_{4}\rightarrow CaSO_{4}+2H_{2}O\Delta H_{r}=206kJ/mol$
and a total of 1840kg(18776 moles) of sulfuric are reacting, the total energy liberated is 3,800,000kJ, which in and of itself would probably damage the structure.

Wickwack, I don't see how your argugment leads to your conclusion. Dilute HCl is used to dissolve messy edges on brickwork therefore if any common acid has any effect on concrete or brick, it will be too slow and feeble to have any significance? Dilute HCl is a long way away from concentrated sulfuric acid. You can't even dip a paint brush into sulfuric without the whole thing just about dissolving. Also it turns wood to charcoal by dehydration, so wood doesn't have much resistance to it at all. 203.27.72.5 (talk) 01:46, 12 June 2012 (UTC)

Wow, that's a lot of answers! Thanks Stu for numbering the questions, I was having a bit of a train of thought and it all came out in a bit of a jumble. The story's going to involve repeated application of acid; say if there was acid falling from the sky on a fairly regular basis, how long would it take for a building to be damaged beyond the point that it offers a reasonable amount of shelter- months, or years? Morgana Fiolett 07:55, 12 June 2012 (UTC)

As can be gathered from the various answers above, that would depend on a lot - type and concentration of acid, whther the building has a clay tile roof, galvanised steel roof, colour bond roof, etc, and whether the structure is Georgina style (ie no overhang to keep the acid rain off windows, doors, and walls), or has a roof overhang. It could range from minutes to years (or longer - acid rain occurs is some areas due to air polution - damge to buildings due to this takes decades and more). Perhaps you could tell us what you want plot wise, and we can then say what in the way of acid type and quantity is needed to do that. Wickwack124.178.61.192 (talk) 10:19, 12 June 2012 (UTC)

Basically, my premise is a post-apocalyptic scenario involving effectively actual acid rain; my survivors have to move from building to building in clear spells in search of ever-rarer safe shelters as the buildings gradually disintegrate. I want them to be able to survive for fifteen-twenty years though; I don't know whether to have the rain getting stronger at times than others, or more frequent, or whether to have it shifting areas so that they can find some areas that have less damage than others? (There's a trope about an isolated valley in there somewhere, I'm sure.) If there was normal rain falling in between acid rainfalls, would that alleviate the effects? The only character with any scientific knowledge is a weatherman, who can forecast the acid storms with some accuracy, but they won't know how it actually came about. At the beginning of that 15-20 year time scale there are plenty of buildings with adequate shelter so they can choose the ones with the most suitable facilities, but at the end of it they should be racing against the storms in hope of getting to the one building in reach that's more solid than the one that just practically fell down around them... As it's fiction, I just need something vaguely plausible, but if this sounds scientifically impossible, I'll have to reassess my plot and go for something over a more condensed time scale. Morgana Fiolett 14:12, 12 June 2012 (UTC)

For what it's worth, almost any roof under normal circumstances has a life expectancy of between 15 and 50 years from the time it's installed, the low end being a standard asphalt shingle or mopped-asphalt roof, and the upper end being copper, lead or tile roof. Some could make it to 100 years between major repairs. That's with normal climatic conditions. In this case, I mean "roof" to be the water-resistant membrane, not the structure, since a building's of little use even if structurally sound if the roof leaks in a general way, particularly if the leakage is toxic. I think your 15 or 20 year time frame would work for the purposes of your story as leaks develop in more cheaply-built materials relatively quickly, which would have a deleterious effect on the structure over a period of years. It's worth mentioning that even in usual circumstances, abandoned buildings deteriorate rapidly. Here's what Chernobyl looks like after 25 years [2]. A search for photographs of abandoned buildings will give you an idea of what happens: Detroit is the poster child for this sort of thing. Plain old water's pretty insidious. Acroterion (talk) 15:38, 12 June 2012 (UTC)

Now that I know what you're writing about I have a story that's much more relevant. My lab has some very badly designed fume cupboards. The scrubbers are woefully undersized for the volumes of acid vapor that get sucked up when we're digesting material for analysis. As a result, a lot of acid vapor makes it up into the flues of the roof and condenses either on the pipework or in the air, and settles back down on the roof in a fine mist.

Up until recently the roof was made of corrugated galvanised iron. This was eaten away by the acid at such a rate that it needed to be replaced once a year. The corrosion was heavily dependent on the seasons; in the wet season, the roof was fine as it was constantly being rinsed by the rain. In the dry season it corroded very fast, as the vapors would condense instantly upon hitting the cold air outside the flue and you could see the mist form and settle back down. We got tired of replacing the roof so often, so we started using a specially designed, corrugated plastic sheet to cover the iron. So far this has lasted well with no noticeable corrosion.

Before that we tried coating the roof in a marine grade sealant, which didn't really do anything to stop the acid. Another building here affected by acid damage is a shed that stores suldides. The sulfides decompose and form massive clouds of sulfur dioxide. Acid rain is basically caused by sulfur dioxide, so having clouds of it form in the shed and escape through the doors and louvers destroys the structure. It's just been redone recently with the same plasic sheeting as the lab, but a few months ago the panels on the roof and walls were so corroded that many were only held onto the frame at one or two points and they just flapped in the breeze. The whirlybird roof ventilators were rusted into solid clumps of metal and the concrete floor was severely damaged all over.

If there was a literal storm of relatively concentrated acid I'm sure it would destroy many structures in one hit and people would be severely injured. The agitation would ensure a very complete reaction with metals and concrete, and aftwards, the acid on the ground would fume as it all dries up which would gas people breathing it in, even if they were inside (unless there were adequate seals on the door, windows, etc. Agriculture would also be entirely shot. On the other hand, concentrated acid storms are really not likely to happen, and even if they did, the conditions required for them to be a long term feature of global weather patterns would be...improbable. 203.27.72.5 (talk) 22:00, 12 June 2012 (UTC)

Nasty sulphides stored in an obviously inadequate & unsecured manner, replacing roof iron once per year? Must be a government lab. It would have much been cheaper to install proper fume cupboards & chimneys etc rather than replace a building roof each year. Wickwack60.228.240.65 (talk) 01:56, 13 June 2012 (UTC)

It's not a government lab. Yes, it would have been better to install fume cupboards that were up to the task, but the supplier advised that these were adequate, and the previous Chief Chemist took them at their word. The shed has been rebuilt with acid resistant materials, but recently we've found that just storing the sulfides in piles outside is better anyway, because both the heat and fumes dissipate much more quickly. The heat is a problem because it speeds up the reaction so you get way more fumes and the fumes are a hazard to the workers here as well as the structures. We're talking about the bulk storage of thousands of tonnes of sulfide ore awaiting transport. I don't know what you mean by saying it's unsecured. Would someone want to steal it? And the storage requirements are met, so whether or not it's adequate depends on who you're asking. 203.27.72.5 (talk) 03:35, 13 June 2012 (UTC)

Hi energy protons direct conversion into electricity?

The article Helium-3#Power generation mentions direct conversion of protons into electric energy with efficiencies at 70%, how would such conversion device be built?, a simple metal plate or more complex?

A second-generation approach to controlled fusion power involves combining helium-3 (³₂He) and deuterium (²₁H). This reaction produces a helium-4 ion (⁴₂He) (like an alpha particle, but of different origin) and a high-energy proton (positively charged hydrogen ion) (¹₁p). The most important potential advantage of this fusion reaction for power production as well as other applications lies in its compatibility with the use of electrostatic fields to control fuel ions and the fusion protons. Protons, as positively charged particles, can be converted directly into electricity, through use of solid-state conversion materials as well as other techniques. Potential conversion efficiencies of 70% may be possible, as there is no need to convert proton energy to heat in order to drive a turbine-powered electrical generator.

Electron9 (talk) 20:31, 11 June 2012 (UTC)

I don't really have any idea if this would work, but I imagine a coil of wire with the proton beam path as a tangent to the coil. As the protons move past they drag electrons with them and induce a current through the wire. 203.27.72.5 (talk) 03:39, 12 June 2012 (UTC)

One way is to have the protons leave one electrode and head for another one and then impact it. The other electrode will be at a high positive voltage, so that the proton loses velocity and impacts at low speed. However this is unlikely to be practical for voltages much above 1 million volts, and you really have to get the protons moving in one direction, and any fast electrons going in another direction. Having a variety of energies mean that some higher energy protons will have energy wasted, and low energy protons may not reach the electrode. Graeme Bartlett (talk) 10:58, 12 June 2012 (UTC)

air bag safety

I am trying to find the minimum weight and height for a child to safely sit in the front seat of a car with an airbag. All I can find so far is Yahoo! Answers or else "check with the vehicle's manufacturer" and I want to know what either the Canadian or U.S. government safety recommendations are. Many thanks! I have a reference question (talk) 20:36, 11 June 2012 (UTC)

The danger is that the airbag will only hit their head, and not their chest, and thus break their neck. So, how high the child's head is above the seat is important, and this would be affected by the use of a booster seat, whether the car seat is adjusted all the way up (assuming it has an up-down adjustment), and the model of the car. So, it probably doesn't depend on their weight as much as their height, and those other factors I mentioned. Also, some airbags have a slower inflation setting for children, which allows them to be used for younger kids. So, unfortunately, the model of the car is a critical part of the decision. StuRat (talk) 22:20, 11 June 2012 (UTC)

According to the U.S. Centers for Disease Control and Prevention website section "Child Passenger Safety": "All children younger than 13 years should ride in the back seat. Never place a child in the front seat facing an airbag." See also safercar.gov at "Air Bag Safety".

• Yale School of Medicine says more specifically:"In fact, no child younger than 13 or under 65 pounds should sit in the front seat of a car equipped with passenger-side air bags, according to both the Department of Transportation (DOT) and the National Transportation Safety Board (NTSB)" here "Air Bags: Not for Children". Nb. found by 'Googling' "air bag children" - 220 of ^Borg 16:26, 13 June 2012 (UTC)

How will Venus to survive tip of RGB

From the youtube I saw [3] two guys from UC Berkeley demonstrate the reasons Earth will escape enough to avoid engulfment over RGB, is it still possible enough from Venus to expand its orbit enough so it misses over tip of RGB's engulfment. Since this site said Venus is most likely swallowed up, is it still currently possible for Venus to escape enough to avoid destruction? Is tip of RGB definitely 1.2 AU, and loss sun's mass definitely 33%, or is it just part of Dr Smith's calculation. Do other guys agree with the same calculation or people come up with different calculations every year? Is it also possible for sun's tip of RGB to miss Earth's orbit by degrees of fractions, because at 1.2 AU solar radius, it is unlikely for Venus to avoid engulfment. Can tip of RGB make sun lose to more than 42% of the solar mass? When you look at the similar stars going through the similar fate, how will you only get the estimates, is the estimates more direct or the information from foreign stars is still chaotic?--69.226.45.43 (talk) 20:38, 11 June 2012 (UTC)

I'm not sure we have all that reliable predictions as to what will happen. As you have noted, some estimates say Earth is toast; others say it will survive. I think the best we can say is that, being closer, Venus stands less of a chance of surviving, but there is no perfect prediction one way or the other. --Jayron32 20:43, 11 June 2012 (UTC)

Not that I don't enjoy these kind of questions, but any reason you're so interested in this topic? As I've mentioned before this is an event extremely far in the future that has an incredible amount of uncertainty in it, so there's not much that we can say definitively. I wouldn't even go as far as to say that Mercury won't escape; it's certainly possible! Again, not criticizing, just curious as to why you're so curious.-RunningOnBrains^(talk) 22:14, 11 June 2012 (UTC)

Me and my stupid summarizing mind, I failed to read your whole question. I'm not sure the exact uncertainty involved in these calculations, but I suspect they are quite large (possibly as large as you allude to above). I'll see if I can dig up some exact figures later today. -RunningOnBrains^(talk) 22:19, 11 June 2012 (UTC)

I wasn't really paying attention for first. I just talking too much about why earth will be swallowed up just because Dr. Smith's variable coming up later. I didn't know this site still exist. Is there any difference between Second Red Giant Phase and Asymptotic Giant. The Pogge's calculation calls it Second Red Giant Phase but Smith calls it Asymptotic Giant, I am not sure which way should I identify it. I thought Asymptotic Giant is not a Red Giant.--69.226.45.43 (talk) 22:25, 11 June 2012 (UTC)

There are probably hundreds of scientific papers on this topic and they all make different assumptions and therefore reach different conclusions. The only definitive answer anyone can give you is the same answer you've been given every other time you've asked these questions: nobody knows. --Tango (talk) 01:14, 12 June 2012 (UTC)

No offense, but unless you are an astronomer this question is pointless for you. If you are an astronomer, then you are perfectly capable of answering the question yourself. Regardless of whether the Earth gets engulfed or not, its surface temperature is certain to rise over 500°C, making it uninhabitable. Anonymous.translator (talk) 01:45, 12 June 2012 (UTC)

Okay I got it clear now. Thank you all for your help and the time in clarifications.--69.226.45.43 (talk) 02:09, 12 June 2012 (UTC)

When the sun swells up there will be a lot of tidal drag on the planets that will slow them down and let them fall in, and once they are in the solar envelope, there will be a bow shock wave that also causes more dragging and spiralling in. Once in the sun's atmosphere the planets will not be vapourised immediately but will take thousands of years to do so, when the planet gets deep inside the evaporation will be even faster, and it is very unlikely that the star will shrink back on down and leave a planet corpse behind. If it was left it may just be an iron core. Graeme Bartlett (talk) 10:50, 12 June 2012 (UTC)

It's not certain Venus will exist by that time, see here:

A long-term numerical integration of the classical Newtonian approximation to the planetary orbital motions of the full Solar System (sun + 8 planets), spanning 20 Gyr, was performed. The results showed no severe instability arising over this time interval. Subsequently, utilizing a bifurcation method described by Jacques Laskar, two numerical experiments were performed with the goal of determining dynamically allowed evolutions for the Solar System in which the planetary orbits become unstable. The experiments yielded one evolution in which Mercury falls onto the Sun at ~1.261Gyr from now, and another in which Mercury and Venus collide in ~862Myr. In the latter solution, as a result of Mercury's unstable behavior, Mars was ejected from the Solar System at ~822Myr. We have performed a number of numerical tests that confirm these results, and indicate that they are not numerical artifacts. Using synthetic secular perturbation theory, we find that Mercury is destabilized via an entrance into a linear secular resonance with Jupiter in which their corresponding eigenfrequencies experience extended periods of commensurability. The effects of general relativity on the dynamical stability are discussed. An application of the bifurcation method to the outer Solar System (Jupiter, Saturn, Uranus, and Neptune) showed no sign of instability during the course of 24Gyr of integrations, in keeping with an expected Uranian dynamical lifetime of 10^(18) years.

Count Iblis (talk) 19:16, 12 June 2012 (UTC)