Wikipedia:Reference desk/Archives/Science/2013 January 17

= January 17 =

Nickel replacing magnesium in geoporphyrin
The geoporphyrins - see Abelsonite - have formed from chlorophyll in fossils of plants. However, the Mg ion is replaced by Ni or V ion. What is the mechanism for Mg replacement with Ni or V? Namely, did this somehow happened after fossilization (how?) or did the original plants have Ni or V ions in their photopigments? Or maybe only the few porphyrin molecules that had Ni or V ion at the center of the ring survived until present, and the ones with Mg (or Fe) ion did not? Our article Porphyrin seems to suggest that Ni- and V- containing porphyrins in oil and oil-shale came from bacteria and not from plants. Indeed, corphin has Ni ion at the center of its porphyrin ring. On the other hand, this paper suggests that the plant chlorophyll is the origin of the porphyrin in oil, and does not explain how Mg was replaced by Ni. So what`s the answer? Thanks in advance, --Dr Dima (talk) 00:43, 17 January 2013 (UTC)


 * It could be post depositional ion replacement, if Ni or V ions have radii compatible with the porphyrin ring, then given the right chemical conditions, it will replace the magnesium. This would explain the rarity of the mineral, the conincidence of porphyrin and soluble Ni or V salts. Plasmic Physics (talk) 09:00, 17 January 2013 (UTC)

Atomic/Ionic Radii
Why is it that the atomic radius of fluorine (64pm) is less than the ionic radius of the sodium ion (98pm on the IB Chemistry data booklet, various values around/over 100pm in wikipedia articles, but in any case, still far greater than the atmoic radius of fluorine)? Applying a Bohr-Rutherford diagram (which I understand is a simplistic/somewhat inaccurate representation), it would appear that the sodium ion has a greater nuclear charge than fluorine, and the same number of electron shells. The nuclear charge, as I've been taught, overcomes the repulsion created by increased electron-electron repulsion, which should therefore lead to a smaller radius (neon illustrates this trend, as its radius, 58pm, is smaller than that of fluorine, and it has the same differences with fluorine as the sodium ion does (although neon does have 1 fewer proton)). I've asked around, and someone suggested it may have something to do with sub-levels (which I have not learned but sort-of understand through my own reading), although I do not see how this explains it. Could someone offer an explanation? (all group 1 ions appear to be smaller than group 17 and 18 atoms).  Bramble  claw  x   02:09, 17 January 2013 (UTC)
 * You're likely measuring apples and oranges here. Atomic radius is a fuzzy concept (because atoms are fuzzy concepts) and there can be a great varience in how radii are measured or defined from one method to another.  The Van der Waals radius of an atom derived the Van der Waals equations of state for a gas-phase atom is not going to be a compatible measurement to the Ionic radius, which is measured empirically from the crystal lattice via X-ray crystallography.  Different measurements measuring different things in different ways cannot be compared quantitatively.  -- Jayron  32  02:59, 17 January 2013 (UTC)
 * Thank you. I guess I was just focussing too hard on there being a definitive boundary, hm?  Bramble  claw  x   00:54, 20 January 2013 (UTC)
 * You should be measuring the ionic radius and not the atomic radius for F to compare this. Currently you are comparing the radii of F and Na+. Shannon gives rion(F−)=119 pm and rion(Na+)=116 pm. Double sharp (talk) 15:34, 18 January 2013 (UTC)
 * As a matter of fact, I fully intended to compare F and Na+. I am aware that F- is indeed larger, but I was hoping to understand why sodium ion was bigger than fluorine atom, with a basis in what I've learned supposedly affect these things: "nuclear charge", "electron shell shielding", "electron-electron repulsion" and "number of shells".  Bramble  claw  x   00:54, 20 January 2013 (UTC)
 * All of those things are real effects; its just that the methods for measuring these things are not as simple as "fetch a ruler". Hypothetically, if you could measure neutral F atoms and Na+ ions using the exact same method, you would get the results you expect.  It's just that there is no simple means to do that.  There isn't even a real "ionic radius" of Na+; each ionic lattice that the ion exists in will have a different effective Na+ radius; this is actually explained in the article ionic radius.  -- Jayron  32  02:14, 20 January 2013 (UTC)

Olive-colored matters in cooked crabs and crayfish
When you peel open the shell of a crab, you'll see some soft olive-colored matter in the shell, mostly on the sides. What is that? Is it supposed to be edible?

When you pull the head of a cooked crayfish off its tail, it'll expose some olive-colored matter, soft and perhaps runny—something that seems to be in the head before. Again, what is that? Is it supposed to be edible? — Preceding unsigned comment added by 71.185.166.208 (talk) 04:33, 17 January 2013 (UTC)
 * I think what you are talking about crab is hepatopancreas, also known as tomalley. --PlanetEditor (talk) 04:45, 17 January 2013 (UTC)
 * And I've eaten them (in lobster, crayfish, and blue crabs) and suffered no ill effects. Eating crayfish has a bit of a ritual associated with it ("suck the head and pinch the tail").  this video shows the procedure, the "suck the head" portion of the procedure involves extracting the tomalley from the crayfish.  Being essentially liver, tomalley/hepatopancreas has the same sorts of health risks associated with eating liver; if you consumed a bowl of the stuff every day for breakfast, it may be unhealthy, but in moderation (which is how often most people eat these foods; they aren't every day staples) you'd be fine.  The Wikipedia article on tomalley notes that there have been health warnings against eating the tomalley of specific shellfish at specific times, but this is often associated with red tide; that makes sense as the liver is basically a filter organ, and thus when there are higher-than-normal levels of toxic substances in the water the lobster is living in, there's going to be more of that stuff in the tomalley as well.  -- Jayron  32  05:28, 17 January 2013 (UTC)

Perception of time between age groups?
I recall watching a tv show where Michio Kaku introduced an experiment that tested the perception of time under duress (does time really slow down during an accident, for example). But I'm wondering if there have been any experiments on the perception of time between different age groups? For example, as a child, I clearly recall getting up, going to school—which dragged on forever—but then in the afternoons, you cram in as much adventure as you can, and you were able to do so. Decades later, I notice I'm getting ready for bed every day, but it feels like I just did that, even though it was 24 hours ago. Adults are always saying how fast time flies. Is it simply due to a difference in, say, stress? I'm very curious, though, if there've been actual (and good) studies on this. – Kerαu noςco pia ◁ gala xies 06:31, 17 January 2013 (UTC)
 * Original research: When I was a child, half an hour would seem like forever, but now it doesn't seem like a long time at all. And paradoxically, back then I wasn't able to read the seconds on a digital watch because they'd flicker too fast for my eyes, but now I can do it easily. 24.23.196.85 (talk) 06:45, 17 January 2013 (UTC)
 * Wikipedia has an article named Time perception which may provide an interesting launching point for the OP to research the answers to their question, and to other related topics. -- Jayron  32  06:58, 17 January 2013 (UTC)

I have observed that the main reason is that any given period of time, say 24 hours, as a percentage of total life experience decreases as time passes, or I should say as the total time of your life experience increases. This has been cited many times here. Example is 24 hours to a 1 day old is double the total life experience for that baby but to a one month old is 1/30 of total life experience.165.212.189.187 (talk) 15:30, 17 January 2013 (UTC)

Tangerine peel oil and styrofoam cup
I am drinking tea in a styrofoam cup (I know, I know shame on me, but in my defense i usually have a mug) and I have a bit of a cold. So I took the peel of my tangerine and ripped it into small pieces over top of the cup of tea. I could see the oils make film on the surface of the tea and got a good amount of it in my tea. a few minutes later I noticed that the styrofoam cup above the water line has been eaten away! What happened? Is this safe to drink? I wont but just wondering. not necessarily medical advice but if the reaction has leached certain chemicals into the tea the it is just lain facts.165.212.189.187 (talk) 15:22, 17 January 2013 (UTC)
 * I recommend you don't drink it but take it to a toxic waste facilty for proper disposal. Didn't your mother teach you about mixing chemicals? If you pour it down the sink we may end up with mutant marine animals that may take over the world.(kidding)--Canoe1967 (talk) 15:40, 17 January 2013 (UTC)


 * I only know that acid can eat away at aluminium foil. You can't use it to envelope food that carries tomato, lemon, etc. In Catalonia it's traditional to use tomato in all sandwiches. It is still traditional that mothers prepare sandwiches for the their kids, and they have to add a layer of paper between the foil and the sandwich, or switch to plastic films. --Enric Naval (talk) 15:42, 17 January 2013 (UTC)


 * I think you have probably rediscovered Limonene recycling.  Sean.hoyland  - talk 15:43, 17 January 2013 (UTC)


 * I remember using a styrofoam cup full of petrol to prime carburetor once. The cup turned to oobleck very quickly. It was probably some type hydrocarbon in the peel.--Canoe1967 (talk) 15:51, 17 January 2013 (UTC)


 * We're not supposed to give medical advice, but I think we should be allowed to say that styrofoam is not a food, even when dissolved in a hydrophobic oil. Wnt (talk) 16:15, 17 January 2013 (UTC)


 * To enlarge and clarify what Wnt is saying - it is entirely possible for quite a range of oils and related organic chemicals to dissolve or corrode polystyrene. This has nothing to do with acidity, and everything to do with the propensity of non-polar solutes to dissolve in non-polar solvents. Tea is mostly water, which is very polar, with some emulsified fats, which are mildly polar and also not good solvents. On the other hand, vegetable oils are quite good solvents, and mostly non-polar. So they dissolve polystyrene. And no, the resulting mish-mash is not good to drink. AlexTiefling (talk) 16:30, 17 January 2013 (UTC)

Boeing 787 manufacturing locations of windshields and fuel tanks
Didn't see those in the summary at Boeing_787_Dreamliner 20.137.2.50 (talk) 16:22, 17 January 2013 (UTC)


 * The Boeing 787 cockpit windows are made by PPG Aerospace Transparencies.
 * http://www.ppg.com/coatings/aerospace/transparencies1/B787_tb_v9.pdf
 * The Boeing 787 fuel tanks are manufactured by Boeing. --Guy Macon (talk) 16:42, 17 January 2013 (UTC)

Which article is this?
I failed to jot it down. Thanks in advance. |A307525693&v=2.1&u=lom_kentdl&it=r&p=ITOF&sw=w 65.88.88.71 (talk) 22:20, 17 January 2013 (UTC)
 * That site requires a password, which I do not have. Sorry.  If you don't have one either, then WP:REX may be able to help you.  -- Jayron  32  22:26, 17 January 2013 (UTC)
 * I'm not sure exactly how I found it, but I think the article is: . Looie496 (talk) 00:04, 18 January 2013 (UTC)
 * Thank you! 65.88.88.71 (talk) 21:20, 18 January 2013 (UTC)