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

= July 11 =

Dangerous Good Classification
I've been asked to determine the amount of soluble lead in a mixture of minerals in order to work out its Dangerous Goods Classification. The method is predefined and straight forward, but I'm trying to work out for my own interest how the results of this test enable us to classify the mixture. I'm told that if the concentration of soluble Pb exceeds 5% of the dry mass, then the material is a Class 6.1: Poison. But that class is actually defined as having an oral toxicity of equal to or less than 200mg/Kg in an animal. So I don't see how the 5% number is anything more than an arbitrary cut off. Does anyone have any idea how this works, or better yet actual experience with classifying class 6 dangerous goods? 203.27.72.5 (talk) 04:39, 11 July 2012 (UTC)


 * Well, the higher the percentage of lead, the less you'd need to consume to be poisoned. Presumably more toxic substances would be considered poisonous in lower percentages, so the total amount you would need to consume to be poisoned is the same in both cases.  I'm not sure why they chose 5%, though.  They must have some idea in mind of how much a person (a toddler, a person with pica, etc.) might reasonably consume. StuRat (talk) 05:47, 11 July 2012 (UTC)


 * It's not lead as such though. It's soluble lead. Total lead doesn't even come into it (and it's well over 50% for many of these materials). Is there a known LD50 of "soluble lead" of around 10mg/kg? 203.27.72.5 (talk) 05:55, 11 July 2012 (UTC)


 * Looking at a variety of material safety data sheets, it does seem that the LD50 for aqueous lead is ~10mg/kg in rodents. The precise number varies wildly depending on precisely how the lead has been solubilized. The most lethal forms of lead appear to be those bound to organic compounds. Acute LD50s are missing from MSDSs for simple lead salts, although they include doses that cause illness over time, which is actually quite low. Someguy1221 (talk) 07:41, 11 July 2012 (UTC)
 * Can you tell me what compounds you're refering to so I can look up the MSDSs? This is most definitely an inorganic lead species, most likely a mixture of PbS, PbSO4 and maybe some oxides. 101.173.85.81 (talk) 09:22, 11 July 2012 (UTC)


 * Heavy metals accumulate in tissue, so you can't use LD50 here. "CDC considers a blood lead level of 10 μg/dL to be a level of concern for children. EPA limits lead in drinking water to 15 μg per liter." This is not medical advice. You should consult a trained professional toxicologist for your question. 71.212.249.178 (talk) 17:03, 11 July 2012 (UTC)
 * Actually telling the poster how to categorize a good for shipping isn't medical advice, it's legal advice - still, unfortunately, beyond our purview. However, it sounds like the OP is asking for an explanation of the reasoning behind this rule, not help in figuring out and applying it.  My assumption is that the 5% figure is by weight, and so the rule tells you how much soluble lead there is in a given weight shipped.  If what's being considered is how much lead will leach into the soil around a crash scene if firefighters hose down the burning package, then I suppose that's sort of reasonable if you're considering the fire as being of some set size in terms of mass.  If it's the damage done if the stuff pours out of a hole in the package and a kid skateboarding around the company's loading dock face-plants into a pile of it ... less so, but anything more realistic might be too bureaucratically challenging for all involved. Wnt (talk) 18:25, 11 July 2012 (UTC)
 * To clarify, I'm not the one working out the dangerous goods classification. I'm just providing data to someone, who is passing that data to someone who is working it out. As Wnt said, I'm just interested in how they got the 5% figure from the actual definition. The LD50 is prescibed in the definitions, so if you want to argue that it's not important and we should look at chronic toxicity, take it up with the United Nations Economic and Social Council. It looks like Someguy hit on it above, but I'm still waiting for him to let me know what compounds he looked at the MSDSs for. You don't need to assume that the 5% figure is by weight, I gave that in the statement of the question "5% of the dry mass". And leaching into soils, etc. sounds more like criteria for Class 9: Environmentally hazardous material (although the wikipedia article on that is a bit vague). I don't think specific, plausible scenarios come into it really. It's "just how toxic is it?", not "how likely is it that some one will eat it?". 203.27.72.5 (talk) 20:36, 11 July 2012 (UTC)

Bell / clapper
I have a long case grandfather clock which chimes in a rather tinny way. How can I improve its voice? Kittybrewster  &#9742;  11:02, 11 July 2012 (UTC)


 * Such clocks need regular cleaning and lubrication, but there are fragile parts and delicate adjustments so don't just attack it with oil or WD40. You could cause a lot of damage if you're not careful. Having said that, before calling a professional I would visually inspect the mechanism to ensure it is clean and that the hammer(s) and gong(s) (it's unlikely to be a bell and a clapper) are moving smoothly and not fouling anything. The hammer should only touch the gong momentarily, not come to rest on it. If there is a pad on the hammer it might need replacing.--Shantavira|feed me 11:44, 11 July 2012 (UTC)


 * On this page you can hear grandfather clock chimes and identify your own, probably the Westminster chimes. Here is a video that shows the chiming mechanism of an (unspecified) grandfather clock receiving attention. If yours is like this, check that the tubular bells hang freely. Other videos on the linked YouTube page give insights into other types of clocks. DriveByWire (talk) 14:16, 11 July 2012 (UTC)


 * You may also have spiderwebs, dust bunnies, or even a crack in one of the noise making parts.--Canoe1967 (talk) 15:42, 11 July 2012 (UTC)


 * Can you identify what's wrong with the sound ? Different sounds may indicate different problems:


 * 1) Short decay: If the sound quickly stops, this could be a sign that it just needs cleaning, as all that dust may dampen the sound. Or, perhaps the gong is attached to something which absorbs the sound too quickly, like wood.  This could be the result of a poor repair job.


 * 2) If you are hearing multiple strikes instead of one, then either the hammer is hitting more than once or the gong is hitting something else.


 * 3) Out of tune: Likely because the mass of the gong is off. Again, this could be due to a poor repair job, say if they attached it with a different fastener than the original.


 * 4) Buzzing: Could indicate a crack in the gong, in which case it would need to be replaced (they could try repairing it, but it will probably never sound quite right). StuRat (talk) 17:58, 11 July 2012 (UTC)
 * Perhaps I have misdescribed it. It has one bell which has one kicker whch has no pad on it. Kittybrewster  &#9742;  11:46, 13 July 2012 (UTC)
 * Can you remove the bell easily? If you hang it buy a string and hit it with similar metal as the hammer then you may be able to tell if the wrong sound comes from the bell or the way it is mounted in the clock. The mounting may be worn out or damaged, the bell may be touching something or have dust/cracks etc. Was there a pad at one time possibly?--Canoe1967 (talk) 17:29, 14 July 2012 (UTC)

Ant evolution question
First and foremost I want to make it clear that I accept evolution as a fact. Just have a specific question about it.

I heard that ants evolved from wasps and that certain traits such as stingers which they inhereted from wasps do show up in certain species of ants. So if this is true, it stands to reason that the genes that code for those stingers should be homologous to the genes that code for the stingers on wasps. My question is, are they in fact homologous? My other question is, are ant wings also coded by homologous genes that code for wasp wings? 148.168.40.4 (talk) 14:52, 11 July 2012 (UTC)
 * Our article Ant says "Ants evolved from a lineage within the vespoid wasps.", so what you heard is apparently true. I don't know the answers to your questions for sure, but I would take it that pretty well all insect wings are homologous, and I would think the stings are too. But you need to be careful about your terminology. When you say "are ant wings also coded by homologous genes", this is a misleading simplification: a structure as complicated as a wing will be coded by a huge number of genes, many of which will also control other things quite unrelated to wings. I'm sure there are particular genes without which wings will not form at all, but that does not mean that those particular genes 'code for wings'. --ColinFine (talk) 16:12, 11 July 2012 (UTC)
 * The only way the genes wouldn't be homologous would be if the structures were lost entirely and then reevolved from scratch. Even then, if they still existed, the same genes might be used over again to form the new structures.  In this case the animals are so closely related and the structures so conserved there is no question of their not being homologous. μηδείς (talk) 16:27, 11 July 2012 (UTC)


 * Nesting for clarity, not replying to Colin, heh


 * I don't know if there have been any attempts at mapping ant or wasp genomes and comparing them (AFAIK, only fruit flies have been studied that extensively), but yes they are. We don't need to examine their genes to know that they are homologous every time (since we're not even that savvy yet at identifying specific genes). Most of the times comparative morphology and developmental morphogenesis is more than enough. See our articles for Body plan, Hox genes, and Evolutionary developmental biology. In the same way that human and chimpanzee hands are obviously homologous, so are ant and wasp (and other Hymenoptera) wings and stingers (and legs, and eyes, and jaws, etc.).


 * Note that despite popular misconception, ant "stings" are from the abdomen, not from bites. And these stings can range from being delivered by piercing or being sprayed directly at an opponent. Nevertheless, both ant and wasp stings come from the same structure also present in other insects, albeit highly modified - the ovipositor. And they still function as such in some species.


 * Wings are a special case as they can evolve to be suppressed partially or wholly during development by genetic or environmental "switches". A phenomenon known as polymorphism (as in human sexual dimorphism). In most ants polymorphism is exhibited by "castes" where sterile female workers and soldiers are all wingless while the fertile queen and males are winged (at least temporarily). In wasps, some extreme examples are in the family Mutillidae, better known as velvet "ants", whose females are wingless and resemble ants while the males remain winged. Same thing with the chalcid wasps, whose males may sometimes even be neotenic, retaining wingless worm-like forms with the sole purpose of mating with females before the females leave the hosts.


 * Rest assured, like Colin said above, all wings of all insects (not just ants and wasps) are homologous, even in cases where the wings may be reduced to only one pair (with the hindwing having evolved into knob-like balancing structures known as halteres in Diptera, or the forewings being modified into protective armored coverings known as elytra in Coleoptera) or absent altogether. See also Insect wing (particularly the section on its evolution and morphogenesis).


 * Lastly, all ants today evolved from a single ancestor, but you must understand that like how humans did not evolve from chimps, ants as well did not evolve directly from modern wasps. Instead they both share a common wasp-like ancestor. The ancestors of ants, wasps, and bees diverged from each other at around 160 million years ago. Ancestors of eusocial ants and wasps in turn diverged from each other at around 140 to 110 million years ago. The oldest known ant fossil is the Cretaceous Sphecomyrma freyi preserved in amber from ~80 million years ago. Like its name suggests, it was more like a "wasp-ant" in that though it was indisputably an ant (possessing the metapleural gland unique to ants) it also exhibited characteristics which are undeniably from wasp-like ancestors (which includes a retractable sting, among others).-- O BSIDIAN  †  S OUL  16:27, 11 July 2012 (UTC)
 * List of sequenced animal genomes - Several insects have had their genomes sequenced, including several ants and wasps. Unique Ubiquitous (talk) 16:34, 11 July 2012 (UTC)
 * There's a certain amount of philosophy involved in homology, and so peculiar details emerge. For example, Diptera and Strepsiptera both have a pair of wings, they both probably have the vast majority of the controlling genes in common... problem is, one has forewings and the other has hindwings, with the others greatly reduced.  So if you look into the genetics you'll find Ultrabithorax has different effects on these wings, even though at first glance it looked like a homologous network.  Evolution does that a lot, and not always in ways you can see - it can duplicate a gene, use two copies for a while, then one lineage gets one copy and the other gets the other and you're left scratching your head trying to figure out why the genes diverged from one another so much sooner than the animals you're studying. Wnt (talk) 18:15, 11 July 2012 (UTC)


 * Regarding 'ant "stings" are from the abdomen, not from bites', I suppose it can be a bit of both e.g. Oecophylla majors haven't retained a functional sting but they do bite and spray the bite with acid from the end of their abdomen. It looks like this after a few seconds.  Sean.hoyland  - talk 18:53, 11 July 2012 (UTC)


 * I meant that the bite itself is not the one delivering the venom, as most people seem to have the misconception that the venom glands are located at the ant's mandibles like in snake fangs.


 * The bite-and-spray behavior is actually the norm in formic acid-spraying ants (formicines) when dealing with larger animals. While in others, like some myrmicines (e.g. fire ants and bulldog ants) and the primitive ponerines (e.g. trap-jaw ants), they only bite (if at all) to gain a foothold, while injecting the venom (not spraying, though the organs responsible are both derived from ovipositors) with functional stingers. The venom of the latter two subfamilies are also more similar to venom used by wasps, and are often extremely painful and in some cases medically significant.


 * Also, in addition to Wnt, there's also an ancestral third wing pair attached to the first segment of the thorax, which has since been lost in most modern insect body plans. It reappeared among treehoppers as their "helmets" (see picture). Insects, like most higher animals (including humans) are derived from repetitive body segments that later became modified and/or fused as they evolved to become more specialized (traces of that is evident in our embryonic stages). Ancestral insects therefore actually had one pair of "wing" appendages for each body segment (though they were not wings then, of course). They were eventually suppressed by Hox genes (like the previously mentioned Ultrabithorax) for all body segments except two, which eventually became used for flight. Except for treehoppers, apparently, which somehow broke the mold. And given that a third pair was more or less superfluous when it reappeared, evolution got creative with it instead. :P -- O BSIDIAN  †  S OUL  22:22, 11 July 2012 (UTC)

Air Conditioning
Regarding energy usage to cool a home, are the following two situations equivalent?
 * 1 Outdoor temperature = 80º and indoor thermostat & temperature = 72º
 * 2 Outdoor temperature = 81º and indoor thermostat & temperature = 73º hydnjo (talk) 15:09, 11 July 2012 (UTC)


 * No, but many methodologies will consider them "approximately" equal. We have an article on degree days, which links to many related concepts.  Nimur (talk) 15:29, 11 July 2012 (UTC)


 * Both situations have an 8º differential so if they are not equivalent then which will require more energy to maintain? hydnjo (talk) 17:15, 11 July 2012 (UTC)


 * I suspect that the lower temperatures will require ever so slightly more energy, considering that to go from 8 degrees above absolute zero down to absolute zero would require an infinite amount of energy. StuRat (talk) 17:46, 11 July 2012 (UTC)


 * True. See Carnot engine for the formula, which is indeed based on a ratio of temperatures in kelvins.  That formula describes how much energy you can extract by reversing the process, which for a perfect air conditioner is theoretically equivalent.  A specific, real air conditioner, with real coolant with a real boiling point, will act differently from that, however, and I can't tell you how. Wnt (talk) 18:01, 11 July 2012 (UTC)

In general, engines work at higher efficiency in a lower ambient temperature, so the air conditioner working in 81 degree weather is slightly less efficient. The inside temperature change gives the target amount of energy which has to be spent, which simply requires it run a certain amount of time, and is not relevant to the efficiency of the engine sitting in the unchanging heat outside the window. Strictly speaking, the heat capacity of air does change by a very small amount, so the amount of energy needed to be expended will differ as the cooler air has a higher heat capacity. This is no where near the difference you run into at the heat of condensation of the boundary conditions of solidification or absolute zero. There is no way to calculate which is greater, the better efficiency or the greater work at the lower temperature, without the specifics. But my gut feeling is the difference in efficiency will be higher, given most air conditioners are inefficient, and it will take more input energy to cool from the higher temperature. μηδείς (talk) 20:08, 11 July 2012 (UTC)


 * Think the answer here lays in the laws of Thermodynamics. As one learns when at school: it is easier to add heat to something that is already hot than to something that is cold – thus the revers is true also. So, as the temperatures drops (regardless of ∆t remaining constant) the efficiency must drop. Ergo, case 1... “Outdoor temperature = 80º and indoor thermostat & temperature = 72º” will require more energy to maintain the same temperature differential (∆t) than case two. --Aspro (talk) 22:35, 11 July 2012 (UTC)


 * I think, Aspro, you might be thinking about the heat of fusion of ice, which much requires more energy to melt a solid liter of ice entirely to water at a constant 32 degrees than to raise a liter one degree from 32 degrees to 33. There is no law that says it is easier to heat hot things than cold ones.  That being said, according to Thermal efficiency air conditioners aren't strictly rated by efficiency, since they are not heat engines. μηδείς ([{User talk:Medeis|talk]]) 01:50, 12 July 2012 (UTC)
 * No. I said what I meant.--Aspro (talk) 01:53, 14 July 2012 (UTC)


 * Case 1 (80/72) is essentially the more efficient for refrigerative airconditioning. This is partly because of the charecteristics of compressors and refrigerant fluids, and partly because the saturation moisture contaent of air is less at lower temperatures - saturation conditions exist at the evaporator, thus less work is done removing moisture at lower temperatures.  Manaufacturers of compressors provide curves of efficiency vs evaporator and vs condensor temperatures in their application datasheets - these always show greater efficiency at lower temperatures.  However, in practice you can get some anomallies as the compressor is normally cycled on and off by the thermostat.  Each time the compressor is started, it works inefficiently for a while until refrigerant conditions are stabilised.  Ratbone58.167.247.229 (talk) 02:05, 12 July 2012 (UTC)

The genesis of this question lies in my wife's insatiable desire to lower our A/C thermostat a degree or two (over which I have no control) and my energy conscious self's justification that its the same as though the outdoor temperature (also over which I have no control) had risen a degree or two. Thanks all for your thoughtful responses, I guess should find something more profound to worry about :-) hydnjo (talk) 23:09, 12 July 2012 (UTC)
 * In which case you asked the wrong question. Lowering the cooled space temperature further below the outside temperature will always increase your electricity consumption.  Figures typical of domestic airconditioners having a COP of around 2.5 and using a common refrigerant:  With an outside temperature of 80 F and decreasing the internal temperture from 72 F to 70 F will increase the amount of heat to be shifted by  (80 - 70)/(80 - 72) i.e., an increase of 25%.  To do this, electricity consumption will have to rise, but not quite 25%, as the lower evaproator temperature will increase efficiency - electricity consumption will rise about 23% or so.  Now, if the set point is left at 70 F, and the outside temperature drops to 78 F, the amount of heat to be shifted drops back to the same amount as before.  However, the lower condensor temperature also improves efficiency, so electricity consumption will fall a bit more than 25% - it will now drop about 27%, so your electricity consumption will be about 96% of the 80/72 case  (not counting anomallies due to cycling).  Ratbone124.178.45.153 (talk) 10:06, 13 July 2012 (UTC)
 * Ratbone, he didn't ask the wrong question. He understands that lowering the thermostat increases energy consumption. He's just rationalizing it by saying that it would have been the same if the outside air temp increased by the same amount. His question was just about whether or not that logic is actually correct. 203.27.72.5 (talk) 22:35, 13 July 2012 (UTC)
 * Well stated but I prefer intellectualizing ;-) hydnjo (talk) 01:42, 14 July 2012 (UTC)
 * Ratbone, no I don't think so. The question I posed was Out > In = 80º > 72º vs 81º > 73º. In both cases the outdoor temperature is 8º warmer than the indoor temperature. I arbitrarily chose both the outdoor ∆t = 1º and the Out > In ∆t = 8º for illustration and ease of calculation. hydnjo (talk) 13:14, 13 July 2012 (UTC)

Neutralize soap?
What's the most effective way to neutralize liquid soap that has been spilled inside a rucksack (unwashable) ..? Electron9 (talk) 18:44, 11 July 2012 (UTC)


 * Does 'unwashable' mean it can't get wet or can't handle the punishment of a machine? If it can handle warm water you could just soak it until the soap dissolves and dilutes. The warmer the water the faster it will work. You could try dry cleaning but that may be a cost issue. If there is perfume in the soap that may last longer but should go away by September when school starts.--Canoe1967 (talk) 18:57, 11 July 2012 (UTC)


 * It means it should not be put in a machine because the water protection may suffer. And the protection may have chemical components that I don't want in the machine. So I thought about something chemically better than plain hot water. Electron9 (talk) 20:33, 11 July 2012 (UTC)


 * In that case, you can go ahead and machine wash it, then spray it with water-proofing agent after it dries. (You should be able to buy that at a shoe store.) StuRat (talk) 20:36, 11 July 2012 (UTC)


 * Does unwashable mean unsoakable and unrinsible? 71.212.249.178 (talk) 19:07, 11 July 2012 (UTC)


 * I'd first physically remove as much as possible, with a sponge. Then soak it, say in the tub.  You may need to drain the water and replace it several times, until you stop seeing suds.  Tumble dry on low heat.  (If you literally have a rucksack that falls apart if it gets wet, on the other hand, then throw it out and get a better one.)  StuRat (talk) 19:11, 11 July 2012 (UTC)

If it has leather parts you may wish to treat those with leather water-proofing, etc. first. Can you get a manual for your pack or a similar one that says how to treat the leather?
 * The number one best chemical to neutralize soap is water. Think about it. What other kind of substance could you imagine that isn't it self going to be a pain (or require water) to remove? Vespine (talk) 22:51, 11 July 2012 (UTC)
 * To answer your hypothetical, an oil-based substance may be appropriate, especially if the rucksack is leather. Special leather oils are good for leather, and any greasy substance in sufficient quantity will neutralize a soap. I don't recommend blindly attempting this solution in the example at hand, though. BigNate37(T) 22:54, 11 July 2012 (UTC)
 * Make sense as soap decomposes flesh which protect itself with.. oil. The question is then what amount and type of oil. The rucksack is made with textile. Electron9 (talk) 04:05, 12 July 2012 (UTC)
 * If it's textile, then just use water. Otherwise you'll need soapy water to get the oil off it anyway. 203.27.72.5 (talk) 04:11, 12 July 2012 (UTC)

Why are commercial aircraft round?
Couldn't all the Boeings and Airbuses be less like a cylinder and more flat? It seems to me that lots of space gets lot due to this cylindrical form. OsmanRF34 (talk) 22:15, 11 July 2012 (UTC)
 * A round cross-section is the strongest shape, anything ovular would require stronger materials to achieve the same structural integrity. This may be the reason they are round: to minimize structural mass. Granted, I am not an aerospace engineer, nor close to it. BigNate37(T) 22:28, 11 July 2012 (UTC)
 * It's not just structural integrity, but also the ability to stand the overpressure of maintaining close to one atmosphere at a height where ambient air pressure is only ~20% of normal. --Stephan Schulz (talk) 22:32, 11 July 2012 (UTC)
 * How is the ability to tolerate overpressure any different to structural integrity? 203.27.72.5 (talk) 22:39, 11 July 2012 (UTC)
 * Is that why combat aircraft pilots are often seen to be using a breathing apparatus? I.e., to allow the cockpit to have less of a pressure differential without affecting the pilot, because they are too small to be perfectly round? BigNate37(T) 22:36, 11 July 2012 (UTC)
 * Note that they are not perfectly round and are slightly oval in shape. The Embraer E-170 for example is 3.35m high and 3.01 meters wide. 203.27.72.5 (talk) 22:38, 11 July 2012 (UTC)
 * Wide-body aircraft like the Boeing 747 and Airbus A380 are far from round. 203.27.72.5 (talk) 22:49, 11 July 2012 (UTC)

— Preceding unsigned comment added by 203.27.72.5 (talk) 22:51, 11 July 2012 (UTC) They're shaped like beer cans for the same reason. Hcobb (talk) 22:41, 11 July 2012 (UTC)
 * I'd question two premises. One, I highly doubt much space is wasted at all in a modern jet liner. There's an incredible amount of stuff that gets packed into that cylinder. Two, it's not really "space" that is the issue anyway, it's more about weight. Anything that "looks" like wasted space is probably required for access. Don't forget that just about every single component in the plane must be able to be inspected and replaced if required at some stage, so packing everything as tight as possible to save "space" doesn't sound like a great idea for more then one reason. Vespine (talk) 22:47, 11 July 2012 (UTC)
 * Just to second what Vespine said, those "wasted" spaces are filled with things like ballasts and fuel tanks that can take just about any shape you like. The space in a modern airliner is used with efficiency you're not likely to see anywhere else, unless you happen to be flying a bit higher. 203.27.72.5 (talk) 23:01, 11 July 2012 (UTC)
 * Actually, to slightly contradict part of what Vespine said, space is a major issue in addition to weight. Drag is (generally speaking) inversly proportional to density, so unused "wasted" space (if it actually existed) would lower the average density of the aircraft and increase drag. This is obviously all from an initial design of the aircraft perspective. I'm not suggesting that existing aircraft could fill in those gaps with extra passengers' luggage to reduce drag :). 203.27.72.5 (talk) 23:22, 11 July 2012 (UTC)


 * I didn't say aircraft are cylindrical, just like a cylinder. Another point: there is less wasted space because commercial aircraft combine cargo (not related to the passengers flying in it) with passengers as best as it gets. But if it were more flat in the y-axis, you could reduce the cargo space and put more people into it. The resulting aircraft would look more like a big wing (and you could have shorter wings). It's clear to me that there are lots of calculations and reasons for the shape that aircraft have, but I'd be happy with a couple of hints. OsmanRF34 (talk) 23:30, 11 July 2012 (UTC)


 * Something else to consider is the comfort factor in each seat. In the Airbus 380 diagram above, it looks like tall outside passengers on the upper deck will have their necks bent by the fuselage wall.  Passenger comfort alone would dictate a rounded square cross section be used, but anyone who has ever been on an airplane can attest that passenger comfort is obviously only a minor concern. StuRat (talk) 23:53, 11 July 2012 (UTC)
 * Well maybe not anyone. To quote one airline passenger, "If you travel as much as we do you appreciate the improvements in aircraft design of less noise and more comfort – provided you don't travel in something called economy class, which sounds ghastly." 203.27.72.5 (talk) 00:49, 12 July 2012 (UTC)

Size of Earth's orbit last 2000 years
Has the size of the Earth's orbit around the Sun changed significantly in the last 2000 years, as this article says? Bubba73 You talkin' to me? 22:58, 11 July 2012 (UTC)
 * See Earth's orbit. But here's the spoiler: no it hasn't. 203.27.72.5 (talk) 23:02, 11 July 2012 (UTC)


 * Thanks. I thought that it hadn't changed that much in 2000 years, but I don't see anything in that article addressing it.  Bubba73 You talkin' to me? 23:26, 11 July 2012 (UTC)
 * The paper that is described by that Daily Mail article is freely available here. The Daily Mail article is misleadingly worded.  Even though the Earth's orbit has not changed significantly, the precession of the Earth's axis combined with the elliptical shape of its orbit has caused a small change in the distance from the Sun during June-July-August, and that's the change that the authors invoke to account for their data. Looie496 (talk) 23:26, 11 July 2012 (UTC)
 * (See our article on Milankovitch cycles for more information.) Looie496 (talk) 23:35, 11 July 2012 (UTC)

Airliner cabin air
Does the air in an airliner cabin recirculate, or is there some mechanism to exchange it with outside air without losing the cabin pressure? 203.27.72.5 (talk) 23:14, 11 July 2012 (UTC)


 * Humans exhale carbon dioxide (and depending on the in-flight meals... other gases too). This has to be got rid of so stale air gets bleed off. Therefore, air can not be recirculated. The banning of smoking also meant that the amount new air added to the cabin could be reduced -thus saving the costs of pressurizing greater amounts of air to keep the interior atmosphere agreeable. To save more costs, they also reduced (in the last decade), the cabin pressure – but to the detriment of passengers suffering from emphysema and other medical conditions that low air pressure can aggravate. To counter the possible resulting in-flight emergencies from this new practice,  some air-lines are now carrying  portable automatic heart defibrillators on board -as if to say – we endeavour to take great care of our customers as always. I don't know what is better – a twenty cents  cheaper ticket or free electric shocks.Also, On some air-line carriers you might also notice a very  odd smell wafting over you. --Aspro (talk) 23:42, 11 July 2012 (UTC)


 * Ah, are you sure about the trend in cabin pressure? The sources I've looked at seem to suggest the opposite.  (See, for example, cabin pressurization.)  The new Boeing 787 and Airbus A380 have effective cabin altitudes of 6000 ft and 5000 ft, respectively, significantly lower than the 7000-8000 ft seen on older aircraft.  I suspect that you may be the victim of similar misconceptions about the quality of cabin air today versus a decade or two ago.  The amount of air supplied per passenger hasn't changed much over the last forty years; if anything, the banning of smoking aboard aircraft has made the air cleaner for everyone: .  TenOfAllTrades(talk) 00:18, 12 July 2012 (UTC)
 * moved from my talk page: 'Hello Aspro. On 11 July you replied to a question asked at Wikipedia:Reference desk/Science. The question related to Airliner cabin air. See your diff. Your answer included the following statements:
 * The banning of smoking also meant that the amount new air added to the cabin could be reduced -thus saving the costs of pressurizing greater amounts of air to keep the interior atmosphere agreeable. To save more costs, they also reduced (in the last decade), the cabin pressure – but to the detriment of passengers suffering from emphysema and other medical conditions that low air pressure can aggravate. To counter the possible resulting in-flight emergencies from this new practice, some air-lines are now carrying portable automatic heart defibrillators on board.
 * To support your answers you supplied a link to a website that discusses spraying of insecticides on airliners. See your diff. I have looked at that website but found nothing to support the statements I have pasted above.
 * I have also looked at the Wikipedia article on Cabin pressurization but I found no information of the kind you gave in your answer. It looks to me like you have used the opportunity given by this question to respond with some of your original research. It looks to me very much like your own conspiracy theory, or someone else’s conspiracy theory to which you have enthusiastically subscribed.
 * Wikipedia’s reference desks are intended as places where Users from around the world can ask serious questions and receive high-quality answers. I think your answer was a very poor one so I ask that, in future, if you can’t find the answer using the resources of Wikipedia or some other reliable published source, don’t answer the question. Certainly don’t use the reference desks as vehicles for your own original research or your favourite conspiracy theory. Before I write anything more I am interested in whatever comment you wish to make about my criticism. Dolphin (t) 01:07, 12 July 2012 (UTC)


 * To both above comments: The reference to insecticides was an aside for those that did not know about this practice -not support to my previous post. I could have mentioned other forms of chemical  contaminations but they tend not to be intentional.  Second. During the Second World War the Science aviation  Aviation Medicine.  recognised that above 6,000 feet, air crews need to breath oxygen and above 10,000 ft it became mandatory. So with the introduction of passenger airlines with pressured cabins, the design specifications called for 6,000 ft also (whether airline operates choose to use this capability to the full is  a matter of economics). This was long before the  introduction of  the Dreamliner  and A380. However, when fuel costs shot up, many airline sort to save costs by manually reducing the cabin pressures and volume exchange. Here  is a resent discussion on what cabins pressure ought to be., . “Respiratory benefits and costs of returning to the 30% higher outside air ventilation rates and 8% higher cabin pressures of the 1960s and 1970s  are outlined (emphasis mine). .  Maintaining cabin pressure come at no small cost over the operating life of an aircraft, therefore Boeing’s have  designed the Dreamliner so that the air exchange  can be matched to the exact number of passengers on each flight. The figure of 8,000 feet is the  acceptable maximum  and OK for a fit person – some airlines however have been suspected of maintaining lesser  cabin pressures. See:APPENDIX 4: Major destinations exceeding 2438 m (8000 ft) [] Note: This was not  an exhaustive list . This is not OR on my part but recounting worries that have been brought to my attention by friends who have had reason to to battle with their management in  the air transport industry.  With more people flying more frequently, these problems are increasing. Added to that, is the inconvenient times when one's plane gets diverted, due  to a medical emergency suffered by another passenger.
 * Air travel is now incredibly safe due to the development of regulations encouraging good practice but blind trust in believing that   accountants can  run the airlines alone and go along with believing every reassurance the PR department coughs up, is not something your air  aircrew on your next flight maybe happy to go along with – after all, they  often have to deal with life and death decisions and in the worst cast scenario -more likely  hit the ground before you do. --Aspro (talk) 17:07, 13 July 2012 (UTC)
 * Without wanting to get too much in to this discussion, I don't really get the relevence of 'appendix 4'. If you visit a destination with an altitude greater then 8000 feet, of course you should expect to experience cabin 'pressuration' greater then 8000 feet by the end of the journey. This source cited by the same source with the appendix 4 does cite a range up to 8,915 feet although it's from 1988 and mentions the higher crusing altitude of more modern aircraft as a factor for lower pressurations (I didn't look at the source only the abstract).
 * In terms of the rest of the stuff, even one of your sources seems to support the idea that new aircraft are designed to be able to maintain maximum cabin pressurations of 6000 feet through long haul flights which older aircraft were generally not. While you're correct it's not clear airlines will use this, I haven't seen anything from your sources suggesting there has been a recent reduction in cabin pressuration.
 * One of the sources does suggest things were better in the 60s or 70s but both your earlier and more recent comments seem to suggest this as a recent thing as well. Notably if your read that source (well I only skimmed through it), it seems to suggest the difference from the 60s-70s was the inability of aircraft from that time to recirculate air which was done for cost reasons. It does mention a trend through increasing recirculated air. (It mentions there are some advantages to the passenger from increasing recirculated air but from the abstract I guess they concluded the disadvantages outweighed the advantages.) More importantly since I'm only really addressing the cabin pressuration comment, it also seems to suggest that the changes from earlier are because of the increased cruise altitude and you'll need stronger airframes etc to allow high pressuration at the higher cruise altitudes. To this extent, you're correct it's a cost issue but this doesn't really seem to be the manner you were referring to. Notably although I only skimmed through it, while having lower cabin pressurations obviously saves costs, I didn't notice any suggestion there was a concern airlines were raising pressuration to save cost beyond that dictated by the cruising altitude and airframe. The source is from 2002 so I guess lack info one the recent aircraft like the 787 or A380 which sound like the sort of thing they were referring to that would be needed.
 * As a final point unless I missed it none of the sources mention any recent changes in cabin pressuration levels beyond that from the newer aircraft.
 * As to what you've heard from the industry, I can't comment on that although I admit I'm somewhat dubious about things heard in the 'industry' which no one else seems to know. I would at least expect these to show up in non-RS (forums etc) and probably even the odd RS. (I'm not saying they don't exist, simply that without them I don't find your claim particularly credible.)
 * Nil Einne (talk) 08:46, 14 July 2012 (UTC)


 * So, is it that some of it recirculates and some is bled off and replaced? And how does the mechanism work that replaces it? It must be some sort of compressor I take it. Does it work a bit like a ramjet or is it just a normal air compressor? 203.27.72.5 (talk) 00:35, 12 July 2012 (UTC)
 * The turbine engines that drive modern airplanes are giant air compressors. Air is bled from the compressor stage of the engine and cooled in a heat exchanger; and then it is fed into the cabin, both to keep it pressurized and to replace air that is vented from the cabin in the interests of eliminating carbon dioxide, moisture and odours. Some older airplanes, such as the Vickers Viscount, obtained their air for ventilation and pressurization from blowers - mechanical compressors attached to the engine. Dolphin  ( t ) 00:45, 12 July 2012 (UTC)


 * Depends on the cut off line on the word 'modern'. Pressurizing cabins from the engines, can and has lead, to contamination from the engine oils. Example:  www.corporatewatch.org/?lid=3073 . The Boeing Dreamliner for instance, now  gets round this by going back to the old system of having a competently separate compressor.   “In the no-bleed architecture, electrically driven compressors provide the cabin pressurization function, with fresh air brought onboard via dedicated cabin air inlets.”  --Aspro (talk) 23:13, 14 July 2012 (UTC)


 * Thanks. 203.27.72.5 (talk) 00:58, 12 July 2012 (UTC)