Wikipedia:Reference desk/Archives/Science/2014 September 10

= September 10 =

dispose of sulfuric acid?
How can you safely dispose of about liter of concentrated sulfuric acid? Bubba73 You talkin' to me? 01:25, 10 September 2014 (UTC)
 * About 2-3 pounds of baking soda; added slowly and carefully. Or anything mentioned here.  Though the baking soda is probably a bit more fun. -- Jayron  32  01:48, 10 September 2014 (UTC)


 * A hazardous waste depot? -- Consumed Crustacean (talk) 01:51, 10 September 2014 (UTC)


 * Both the above make sense. If you want to neutralise it with minimum drama I'd think about slowly adding it to water first, then adding the reagent. This all depends on how concentrated it is, of course. Greglocock (talk) 02:13, 10 September 2014 (UTC)
 * Think about it, but don't do it! Adding concentrated acid to water may cause an exothermic reaction resulting in a very bad day. 71.20.250.51 (talk) 02:30, 10 September 2014 (UTC)
 * I was always taught "you're doin' whatcha otter when you add the acid to the water". But I offer no warranty on that bit of wisdom. --Trovatore (talk) 02:35, 10 September 2014 (UTC)


 * That's why I said " slowly adding it to water". http://chemistry.emory.edu/home/assets/documents/wastedisposal.pdf "If the acid or base is highly concentrated, it is prudent to first dilute it with cold water (adding the acid or base to the water) to a concentration below 10%. ". You were wise to edit anonymously, 71.20.. Greglocock (talk) 03:26, 10 September 2014 (UTC)


 * Mixing sulfuric acid and water generates heat, and mixing it with baking soda makes copious bubbles. I would mix baking soda with water in a large bucket that is impervious to sulfuric acid, fill it no more than halfway. Then slowly pour the sulfuric acid into it waiting for the bubbles to go down each time. You may wish to have a stirring stick available to speed up the process. A defoaming agent would be good but I don't know which are safe with sulfuric acid. (If you notice it stops making bubbles be concerned that you may have used up all the baking soda.)
 * Alternately get some dilute sodium hydroxide and mix with that instead, no bubbles. Ariel. (talk) 18:47, 10 September 2014 (UTC)


 * It would be safer to dilute the acid first and then add an aqueous solution of baking powder slowly. Greglocock (talk) 23:18, 10 September 2014 (UTC)


 * How is that safer? You are making acidic bubbles if you do that. Plus any acid caught the bubble might not be neutralized since bubbles doen't mix well. Ariel. (talk) 23:54, 10 September 2014 (UTC)


 * The idea behind adding the acid to water (and never water into acid) is that when the reaction gets going, there is a lot of heat generated and there may be splashing and bubbling.  When that happens, you'd rather it was slightly acidic water that was boiling and splattering and not concentrated acid.  The mnemonic I was taught was to use the direction of the alphabet A=>W and not W=>A.   Personally, visualizing the consequences of getting it wrong is the best way to remember!


 * Acid + Alkali makes Salt + Water - so if you can add just enough alkali to your acid to neutralize the pH, then you can toss it down the drain. However adding acid to alkali - or the other way around - is exceedingly dangerous, you want to add those ingredients into a LARGE amount of water to dilute the reactants and diffuse the heat.


 * I would start with a large bucket of water and add acid and alkali alternately in small quantities, mixing carefully and checking the pH each time around.
 * SteveBaker (talk) 01:18, 11 September 2014 (UTC)


 * I make no warranty that this is safe or legal, but what I'm thinking is that if you must get rid of the sulfuric acid (do you really need to?) then its eventual destination is probably the sewer. (The alternative is pouring it on the ground somewhere you don't care about -- this may seem like a harsh idea but the coal power plants have been doing it to us on a grand scale for so many years we don't even expect fish in the streams any more)  So any means of getting rid of it should involve a sink with the tap on full.  You can slowly pour the acid down the hole, and if you're worried about the overall acidity, introduce any manner of neutralizing agent (baking soda, lime, lye... there are things they sell for you to pour down your sink which are not much less corrosive than the sulfuric acid) at frequent intervals.  Most importantly, leave the water running for a while after you're done.  The main risk I suppose is if the acid finds concrete (which is lime, and neutralizes it...) somewhere that a sewer problem due to its degradation would be your financial responsibility instead of someone else's. :)  But I'd expect if you neutralize the acid 100:1 or more with water that it shouldn't be a major threat. Wnt (talk) 15:27, 11 September 2014 (UTC)

Well, I called the local state Environmental Protection Division and they didn't know what to do with it, but they gave me the number of a waste disposal service. Bubba73 You talkin' to me? 05:04, 12 September 2014 (UTC)


 * Last number on Earth I would have called... I would think an auto shop would have ideas, since they have to get rid of lead-laced battery acid. Wnt (talk) 12:06, 12 September 2014 (UTC)

What is "Elongation in 4D"?
Hi, everyone,

I am processing data from a uni-axial tensile test to determine mechanical properties of a material. The specimen is dog bone with circular cross-section. I am stuck with the term "Elongation in 4D", what does this mean and how to calculate it? Thank you very much. SongJie@NTU (talk) 03:34, 10 September 2014 (UTC)


 * 4 x specimen diameter explained here. Mikenorton (talk) 07:13, 10 September 2014 (UTC)
 * Many thanks. So this 4D is also the gauge length to measure strain, right?SongJie@NTU (talk) 08:21, 10 September 2014 (UTC)
 * That's what the reference says, mentioning that it's the standard way of reporting elongations, but I've never done one of those tests myself. Mikenorton (talk) 08:40, 10 September 2014 (UTC)
 * OK. Thanks a lot :) SongJie@NTU (talk) 09:03, 10 September 2014 (UTC)

Species ID
Hello all! Can some one please identify both the species?

Thanks in advance. Nikhil (talk) 05:38, 10 September 2014 (UTC)


 * Scadoxus multiflorus (Blood lily) and the common myna? Abecedare (talk) 06:29, 10 September 2014 (UTC)


 * Yep, no idea about the flower, but the bird's a flying rat (as some affectionately describe those mynas here in Australia). HiLo48 (talk) 08:53, 10 September 2014 (UTC)
 * This is the Canadian flying rat, I think. And the American. InedibleHulk (talk) 10:07, 10 September 2014 (UTC)
 * I thought this was the Candian flying rat? μηδείς (talk) 18:01, 10 September 2014 (UTC)
 * That's a rat in the same way the Hippety Hopper is a mouse. We may not always see eye to eye with them, figuratively, but the kids who've literally done it generally grow up with a fearful sort of respect. A noble nuisance, like a beaver or moose. InedibleHulk (talk) 15:44, 12 September 2014 (UTC)
 * The plant looks like some sort of onion or chive to me. DuncanHill (talk) 13:56, 10 September 2014 (UTC)
 * Just add, the file description calls it a mayflower, but it doesn't look like any of the mayflowers. DuncanHill (talk) 13:59, 10 September 2014 (UTC)
 * Concur with the allium family. --TammyMoet (talk) 17:37, 10 September 2014 (UTC)

Caviar
Traditionally, caviar is served with a mother of pearl caviar spoon, and people are advised not to serve it with anything metal because apparently this can alter the taste. However, every store I've been to that sells it, does so in a metal tin. Is there a reason why we should use caviar spoons? --Andrew 13:44, 10 September 2014 (UTC)
 * It seems unlikely that we're going to do better than the sourced discussion at caviar spoon, which directly addresses this issue. John M Baker (talk) 14:23, 10 September 2014 (UTC)


 * Cans are often coated to prevent reactions with the food. You can see this even with things like canned tomatoes. They often have a thin coating of a polymer or less-reactive metal. suggests that is indeed the case with caviar. Mr.Z-man 20:31, 10 September 2014 (UTC)
 * I don't think the problem is so much with metals per se, as it is that most metals are reactive enough to react with the food mess with the taste. Off the cuff I'd be surprised if gold caviar spoons would alter the taste, but silver probably could. Double sharp (talk) 15:56, 11 September 2014 (UTC)


 * Pfft, I only eat caviar with platinum spoons. Sagittarian Milky Way (talk) 03:13, 13 September 2014 (UTC)

Equal night after equinox
Here, it's not until 27 September that the night becomes longer than the day, and on the actual equinoctial date, day is nine minutes longer than night. Why? Is this because the Sun is a disc, not just a pinpoint? Nyttend backup (talk) 16:05, 10 September 2014 (UTC)
 * See Equinox. -- Jayron  32  16:28, 10 September 2014 (UTC)


 * I don't think our article does justice to the full difficulty here!


 * There is never going to be a day when the amount of daylight and night are EXACTLY the same total duration within a particular calendar day - that's only an approximation to the truth that was convenient for our ancestors to know when the seasons were falling. They didn't need much precision!  Now that we have clocks and very precise ways of measuring, we can see the reality of the astronomical alignments going on here.


 * "Equinox" is really the point in the earth's orbit where the orientation of the tilt of the planet points along the orbital path. This situation only happens for a literal instant, twice a year.   A microsecond earlier and the axis is very slightly pointing away from the sun and a microsecond later, very slightly towards the sun.


 * The 24 hour day in which this instantaneous event occurs is the day which is the closest to having exactly the same daylight and night durations - but for those durations to be perfectly identical, the precise instant of orbital alignment would have to be exactly at noon...and I mean *exactly* not "within a second" - not "within a nanosecond"...exactly. (Or at least as exactly as you measure your daylight/night durations).    Since the rotation of the earth (the roughly 24 hour period) and the orbit of the earth (the roughly 356.2525 day period) are not perfectly in sync - and there are always slight wobbles in the orbit due to other planets passing by and variations in the precise length of a day due to internal processes in the core and the phase of the moon and such, that perfection of daylight/night equality is impossible.


 * However, if you choose to measure those durations accurate to within a second (for example), then statistically, you'll only see that degree of precision once every few hundred years or maybe every few thousand years (it's hard to do the math - so I'm guessing!). If you need it to be identical to within a second, then maybe you should expect that to happen once every 100,000 years.  But if you only need it to be accurate to within 10 minutes...then most years are going to be good enough to meet that demand.


 * But in truth, with perfect measurement precision - then on one day there is more daylight than night - and on the next day, more night than day...and the exact amounts will vary from one year to the next - and we arbitrarily pick one of those two days to be called "the equinox" even though there is not precisely "equal nox".


 * It does get a little bit more complicated than that.  Depending on which time-zone you live in, the 24 hour "day" starts at a different moment in time...so the degree of "equinoxial perfection" depends on your longitude (how far east or west you are) because that alters what time during the 24 hour day that the instant of axial/orbital alignment happened.  So at points along some meridian (a north/south line) - that moment of alignment happened exactly when the sun was highest in the sky - and for people living along that exact line, the amount of daylight and the amount of darkness during that 24 hour interval surrounding the sun-at-highest-point would indeed be identical.


 * Unfortunately - it's not quite that simple. We have time zones...a man-made jumping of the clock by whole numbers of hours.   So if that line of perfection happens not to be bang in the middle of the time zone, then when our clocks say "noon" can easily be 30 minutes or even an entire hour away from the moment when the sun was at it's highest point - and you'll find that the daylight/night durations are slightly wrong again.   If you happened to be lucky enough to be at the right longitude that axial/orbital alignment moment happened precisely when the sun was at it's highest point - it wouldn't be "noon" because your time zone says that it's only 11:45am or whatever.


 * So you'd have to be both on that exact north-south line where you get the axial/orbital alignment happening when the sun is exactly overhead...AND you'd have to be bang in the middle of the time zone so that your clock says it's exactly 12 noon when that happens.  And now we're back down to something that happens only statistically within some close approximation to a true equinox.


 * So, no - the day and night durations are never perfectly the same - never - can't happen.  They are only the same to within some measurement error - and that error can easily be as long as 9 minutes for some places on the earth, and probably as short as a few seconds every few thousand years for people on some exact north/south line that goes through the middle of a time zone and happens to line up just right that year.


 * It's probably best not to stress out about it! :-)
 * SteveBaker (talk) 14:29, 12 September 2014 (UTC)
 * Just to correct one thing "The 24 hour day in which this instantaneous event occurs is the day which is the closest to having exactly the same daylight and night durations" actually not true. Read the article.  The day when we have the closest to equal time of day and night occurs a few days after said equinox.  But otherwise, you're spot on.  -- Jayron  32  14:42, 12 September 2014 (UTC)


 * Ooohhhh - yes. That means I'm actually wrong - but for a MUCH more complicated reason.


 * Because "day" and "night" aren't defined as starting and ending as the center of the sun's disk crossses the horizon - but rather as the time from when the entire sun disappears below the horizon. That bias makes days longer than nights by the amount of time it takes for the sun to cross the horizon line - which (of course) varies depending on how far north or south you are...which complicates matters still further!   It's also complicated by the refractive index of the atmosphere and a bunch of other ikky stuff.


 * When you're at the equator, the 'twilight' period when the sun crosses the horizon line is shorter than toward the poles...so if "daylight" is defined to include the dawn and dusk twilight periods when the sun is only partially covered by the horizon - and "night" excludes those periods - then the day when the two durations are equal is shifted depending on your latitude. But this is a matter of linguistics, not science.  I bet there are some cultures where 'twilight' isn't linguistically included in whatever word they use for "daylight".  Heck, it's messy enough that English uses "day" to mean both 24 hours and "the interval during which a part of the sun's disk is visible".   (In these posts, I've been careful to use "daylight" when I mean the latter!)


 * So at any given latitiude, the 24 hour period that's closest to equal daylight/night durations is shifted from the day of closest axial/orbital alignment.  But (as you say), that doesn't really alter the problem because on that day when the two periods are closest to being equal, you still have the problem that the beginning and end of the day are defined by messy human conventions - and the moment of axial/orbital alignment isn't going to be perfectly at noon.


 * But doesn't this mean that I can in fact get a perfect equinox if I pick the perfect latitude AND longitude?    If the spot where I'm standing is going to get one second more night than day - then can't I just walk a little towards the nearest pole, and staying within the same timezone and with the same noon-time axial/orbital alignment, get a longer twilight period and thereby adjust my personal day length to achieve perfection?  So long as I'm not already at the equator, I can go toward the equator and reduce the daylight duration and increase the length of the night.


 * So I think I need to change my previous answer!


 * If you're at the right longitude/time-zone to get a pretty decent approximation to perfectly equal day/night durations - then moving south or north should allow you to adjust those times to absolute perfection...which leads me to believe that at any point along some complicated arc that jumps at every time zone boundary there is a perfect equinoxial balance.  That would be an interesting curve to plot!


 * The trickiness here is that the mathematical/astronomical ideals are completely screwed up by weird human definitions of things like timezones and when "day" and "night" are considered to commence.
 * SteveBaker (talk) 15:42, 12 September 2014 (UTC)


 * Steve Baker, you're going to confuse everybody who knows astronomy if you use twilight for "the time when the answer to the question 'has the Sun set?' is 'what part?'". The only time I've ever seen twilight mean when a nano-iota of Sun is visible is the very uncommon solar twilight, which is the Sun being less than 6° high but at least a speck is showing, I think.


 * I know of this, and it still intuitively feels incorrect. It's still "day", though different, and should be called peri-daylight. Maybe others have thought this too and that term has Google hits?


 * I believe length of daylight (or is it "visible daylight"?) sometimes means when the Sun is above -6° no refraction (or 5°10' after the sunset). This is because you can't read or play sports or drive without lights after that when there's no Moon. Well you can still read but not newsprint or normal-sized book type. As opposed to length of day which doesn't include this extra hour of baseball-playing time.


 * Also, I believe it's daytime until the Sun passes behind the geoid as seen from your eyes. The geoid as you might know is just the shape of "0 m above sea level". So technically, you can only see the Sun set over land from a few places like near the Caspian Sea, but not on the Caspian Sea, unless you're above the 8th floor. Almost all ocean horizons go over a week between viewable sunsets at least once a month, even if cloud never blocked one. Places with weak tides see sunsets only when waves are unusually small and it's a near-supermoon level low tide. It's impossible to see the Sun set from orbit if it'll happen over a high tide area. But you can peek your nose above the roof of a 9 story Caspian shore building and see it. If you did, you could see the Sun for a whole ~30 seconds after it sets. Sagittarian Milky Way (talk) 03:09, 13 September 2014 (UTC)