Wikipedia:Reference desk/Archives/Science/2016 October 15

= October 15 =

Would the world be in a worse state if we still relied on horse and cart?
Economically, environmentally etcetera? JoshMuirWikipedia (talk) 02:39, 15 October 2016 (UTC)
 * Sort of a general theme of economics is that making it cheaper for people to do something they already want to do allows them to spend more money on other things. This spurs demand, which spurs hiring, which increases the money available to buy things, which... so on and so forth. It's hard to say precisely how much economic damage would be caused by such a drastic change, but you could imagine a massive collapse of various businesses (caused by the vastly increased cost of travel) would cost jobs, incomes, tax revenues, charitable contributions, and government expenditures on lots of worthwhile things. So, potentially huge. As for environmental issues, horses are pretty awful for the environment, despite being "all natural" (well, so is oil). See for instance the great horse manure crisis of 1894. Someguy1221 (talk) 02:54, 15 October 2016 (UTC)
 * Read this and this and this for some background on the environmental question. We of course cannot answer questions of opinion such as "better" or "worse".  But those articles should help you become more informed so as to reach your own conclusions.  Also consider that the transportation of people and goods by horses is of a smaller scale than other transportation methods, such as rail, air, and road vehicles.  This article covers the amount of goods moved through one country (the United States) by road transport.  One can drive across the U.S. in 3-4 days by automobile.  According to this a horse can travel only about 100 miles in 24 hours under optimal conditions; it would take well over a month to cross the U.S. like that.  Also according to This a horse can at best carry 300-400 pounds for at most 8 hours per day.  You can extrapolate from these calculations what it would take to move goods around the U.S. solely by horse.  Again, "worse" is for you to decide without us telling you.  But I've probably given you enough references to make your own comparisons regarding economic differences between using horses vs. trucks for transporting goods; this also ignores rail and air contributions as well.-- Jayron 32 02:56, 15 October 2016 (UTC)
 * I take that to mean you're excluding steam engines. Checking Google maps, it's roughly 1400 miles (2250 km) from Florida to Wisconsin.  A horse and buggy gets maybe 6 miles/9.5 km per hour.  A single horse with a rider might be able to travel 60-100 km (or 37-62 miles) during a maybe 12 hour period.  Horses have to eat, sleep, and even get additional rest even when not sleeping; cars and trucks just need to refuel.  It's not unreasonable to assume that a horse pulling a cart with cargo might only be able to safely travel six hours.  Even if you had stations for switching off horses and drivers every six hours (and had the swap down to a science), it'd still take about five days to ship oranges from Florida to Wisconsin.  That would be too expensive for (at most) a couple dozen crates of oranges though.  So, most non-canned, non-pickled foods would have to be grown locally, which would increase malnutrition (if not outright starvation).
 * The Mississippi river flows about 1.2 miles per hour, and north to south, so it wouldn't help with oranges. Indeed, it would be useless for anything that can't wait a couple of months (assuming you're sailing and rowing as much as possible).  An enterprising Wisconsin cheese manufacturer might use the ride to age his wax-sealed cheese, cutting down on production time.  Otherwise, the river is useless without steam engines.
 * And it's about 1850 km (or about 1150 miles) from Valencia to London, which includes at least 33.3 km (20.7 mi) of sailing. It took about a week to sail from Tunis to Genoa, which (per Google maps) is just under 900 km (roughly 550 miles).  So, premodern sailors could get about 125 km/75 miles per day on a good day.  If the crew rotates shifts and the weather is good, they should be able to pull 5 km/3 miles per hour, making the English Channel a six or seven hour crossing at best (two days at worst).  Again, assuming you have stations to switch horses and drivers every six hours, have the sailing crew rotate, and everything's down to a science, it's still just over a week to get a crate of oranges from Valencia to England.
 * Since uncut oranges can last just over a fortnight, the 1975 series Survivors might have been exaggerating when one of the characters surmised that none of their children would ever taste an orange; but it would certainly be an exotic, decadent, foreign luxury.
 * And those are the best case scenarios. Realistically, the land travel would probably take two to four times as long.  Ian.thomson (talk) 03:55, 15 October 2016 (UTC)


 * No need for malnutrition. If you can't get your vitamin C from oranges, just eat apples instead.  Vitamin pills might be a good idea, too. StuRat (talk) 17:20, 15 October 2016 (UTC)


 * We know how to travel upriver without steam power. It is slower than downstream but not impossible. Just ask any voyageur. Rmhermen (talk) 04:04, 15 October 2016 (UTC)
 * I knew about rowing, but figured that it'd be unfeasible over the couple thousand miles involved except for very light travelers (like Huck and Jim). The voyageur article's description of the dangers would (under modern legal conditions) render land travel preferable to that.  That said, there were indeed trading posts up the Mississippi, though I expect they'd still have to restrict the goods to something more portable than crates of oranges.  Though there does appear to have been plans for (if not actual use of) animal-driven paddle boats after all, so maybe not.  No idea what the speed would be.  Ian.thomson (talk) 05:20, 15 October 2016 (UTC)
 * If there were real canals, then animals could pull heavy boats. This used to happen in the Netherlands. Rivers would be too shallow on the edge and not have a track on the side for the horse/ox. One person would be needed to steer the boat, and another to make the animal pull. Graeme Bartlett (talk) 11:36, 15 October 2016 (UTC)
 * Without getting into stuff like canals and towpaths, riverine commerce was carried out by hybrid sailing/rowing ships for millennia before the invention of the paddle steamer. -165.234.252.11 (talk) 19:33, 17 October 2016 (UTC)
 * You might find this account of the 1894 great horse manure crisis in London of some interest - http://www.historic-uk.com/HistoryUK/HistoryofBritain/Great-Horse-Manure-Crisis-of-1894/ Wymspen (talk) 11:39, 15 October 2016 (UTC)
 * Actually, that account is based on a 2004 article on fee.org, which cites a source that does not say what fee.org claims it does. And there don't appear to be any references to the GHMC anywhere prior to 2004... DS (talk) 23:07, 20 October 2016 (UTC)

Bubbles on puddles
Why is it that when bubbles form on the surface of puddles during rain, this is considered a sign that the rain will continue? My personal hypothesis is that this indicates that dissolved air is coming out of the water, which is a sign that barometric pressure is still falling (and therefore that the low-pressure system bringing the rain is still on the way in) -- am I on to something here? 2601:646:8E01:7E0B:ADC2:429C:883B:48A1 (talk) 10:11, 15 October 2016 (UTC)
 * What is the basis of your first sentence? ←Baseball Bugs What's up, Doc? carrots→ 11:38, 15 October 2016 (UTC)
 * Yes, without commenting on the factuality either way, I can't say I've ever heard the expression. During a rainfall you're unlikely to see many bubbles just because the water in the puddles would be in constant motion. Or are you talking about during gaps in the rainfall? There are a number of factors that would influence the presence of bubbles, including pockets of air in the soil itself. Matt Deres (talk) 13:04, 15 October 2016 (UTC)
 * I think surface tension traps air under a canopy of water until the bubble bursts due to its own inherent instability. I think the formation of the bubble results from the impact of the raindrop on the surface of the puddle, displacing some water and momentarily trapping some air. Bus stop (talk) 15:32, 15 October 2016 (UTC)


 * Searching for bubbles puddles rain I find half a dozen totally non-reliable sources saying this is a genuine old wives' tale, right up there with the thing about red sky in the morning. As such, well, it has a fair chance of being true. Wnt (talk) 18:08, 15 October 2016 (UTC)

Feynman Lectures. Lecture 31. Sec. 31–2 The field due to the material
I have understood everything except one phrase: "the driven motion of the electrons produced an extra wave which travels to the right (that is what the factor eiω(t−z/c) says)"

I don't understand why does factor eiω(t−z/c) say the wave travels to the right. Why not to the left (as we know that waves are source-symmetrical)? In the case of Sec. 31-2 the position z=0 is the glass plate (not the source S). So to use the shifts of the graphs E(t) and E(r) as proof we should assume where source is situated and in what direction the wave goes. But direction is what we have to prove. Besides it is written in Table 31–1 that z is perpendicular distance from the plate (so positive no matter in what point field is measured: to the left or to the right of the plate).

I understand that if the graph of E(t) is like this, then the graph of E(z) is like this in accordance with Fig. 29–2 and Fig. 29–3 and in accordance with rules of graph transformation (like with y=f(x) and y=f(-x)).

Can somebody explain how does factor eiω(t−z/c) (or Cos[ω(t−z/c)]) prove that direction of wave is rightward? I feel the answer must be simple, but I reached a deadlock. Username160611000000 (talk) 11:51, 15 October 2016 (UTC)
 * If the wave from accelerated electrons of the plate would be moving to the left then the factor would become eiω(t+z/c). Is it correct? Username160611000000 (talk) 15:59, 15 October 2016 (UTC)
 * You're right that "waves are source-symmetrical" in that the general solution to the wave equation is symmetric. Particular solutions need not be; $$e^{i\omega(t-z/c)}$$ describes a right-moving wave because its surfaces of constant phase are $$t-z/c=a$$ for arbitrary a, or $$z=c(t-a)=z_0+ct$$ with a rephrased $$z_0=-ca$$.  --Tardis (talk) 15:00, 16 October 2016 (UTC)

Magnesium sulphate and mineral water
Our article on Magnesium sulphate says "It is naturally present in some mineral waters" with a citation needed tag. Is it possible to state this? I know that magnesium ions and sulphate ions could be present in some mineral waters (those in the town of Bath, for example) - but it seems to me that, unless those are the only salt ions present, then the compound itself can't be said to be present. Is this correct?--Phil Holmes (talk) 12:05, 15 October 2016 (UTC)
 * IUPAC changed the spelling of sulphur/sulphate to sulfur/sulfate in 1980. Sleigh (talk) 12:13, 15 October 2016 (UTC)
 * IUPAC has no authority whatsoever over the English language. (Given that they prefer the atrocious "aluminium", it's a good thing they don't.) --Trovatore (talk) 21:57, 15 October 2016 (UTC)
 * My English dictionary still says sulphur, so that's good enough for me. But can you answer my question?--Phil Holmes (talk) 12:41, 15 October 2016 (UTC)
 * it was actually 1990. DMacks (talk) 21:27, 15 October 2016 (UTC)
 * There are certainly quite a few Br− anions in the sea, but we don't have much of a problem saying that there is common salt (NaCl) in it, right? Same principle. Double sharp (talk) 12:51, 15 October 2016 (UTC)
 * By extension, if the water has unusually high levels of both magnesium and sulfate but not of other ions, one could say "it has high levels of magnesium sulfate" because there's not any other obvious way it could have only these two being high. And likewise if there are lots of ions but those two are present in a 1:1 ratio and no other ion levels provide the correct ratio for this substance one could deconvolute the components. But you're right, that if you toss certain amounts of MgSO4 into certain amounts of ocean water, you can't tell after the fact whether you added MgSO4 to water containing NaCl vs adding MgCl2 into water containing Na2SO4. DMacks (talk) 21:21, 15 October 2016 (UTC)

Mission to Europa
In April 2016 issue of Astronomy, a popular magazine, there is a feature article: "FINALLY. The historic journey to Europa." Europa is a Jupiter satellite of course. They say on page 25 that it will be a flyby mission with 45 revolutions around the moon only because the craft will eventually be destroyed by a powerful electron wind emanating from Jupiter. My questions are: (1) If there is a stable wind of electrons that means that Jupiter must be strongly positively charged and that charge must keep increasing. Is it what's happening? The second question is: (2) "What is the origin of those electrons? Thanks, --AboutFace 22 (talk) 16:32, 15 October 2016 (UTC)


 * We have an article about the mission at Europa Multiple-Flyby Mission (not sure it needs italicizing, but it is in the article) which leads to Magnetosphere of Jupiter, a featured article all about the topic of your question. Give those a look and come on back if there's anything that's still unclear. Matt Deres (talk) 16:36, 15 October 2016 (UTC)
 * I've put a note on the article talk page about the italics. The name is apparently rather controversial. Tevildo (talk) 14:16, 16 October 2016 (UTC)


 * (ec)Could it be that electrons move away from Jupiter at that location, but move towards Jupiter at other locations, in an equal amount, guiding by the Jovian magnetic field ? The other possibility is that the electron wind is in orbit, neither leaving nor hitting the planet.  The actual answer may be a bit of both.  (Hopefully Matt's links answer these follow-up Q's.)  StuRat (talk) 16:42, 15 October 2016 (UTC)
 * The electrons are trapped in the same way as they trapped in Earth's radiation belts: they gyrate around the magnetic field lines while cyclically moving along the lines up and down out the equatorial plane. The word "wind" is a misnomer. Ruslik_ Zero 18:55, 15 October 2016 (UTC)

Loudspeaker's size and weigh
Does a good loudspeaker, one that has deep basses and precise high frequencies, have to be heavy and bulky?--Llaanngg (talk) 17:00, 15 October 2016 (UTC)


 * As far as the bass goes, yes. To reproduce the lowest bass frequencies at a reasonable volume you have to move a lot of air, which means a cone with a large diameter and a long excursion, and the box itself has to be large and rigid. You can lighten it a bit with neodymium magnets and using plywood instead of heavier particle board, but that only helps some.


 * One good way around this is to use high-quality headphones. I highly recommend the Audio-technica ATH-M50. --Guy Macon (talk) 17:21, 15 October 2016 (UTC)


 * There are expensive systems that have good bass and small size, such as this one from Bose: . But, there are limits, which is why built-in speakers on even high-end flat-screen TVs often sound horrid.  The solution, if you don't need much volume, is a good 2.1 plug-in speaker system (right, left, and subwoofer speakers), which can give you decent bass for like $30.   StuRat (talk) 17:24, 15 October 2016 (UTC)


 * No, but it has to be stiff. Unless you have a supply of unobtainium, the necessary stiffness has usually been achieved (as this is the cheapest way) by using materials that are heavy and bulky. In a few cases, esoteric materials (mostly carbon fibre composites) have been used to produce lightweight bass speakers - often as horns (although most horns are used as mid-range drivers, large horns can handle bass). Bose speaker systems have tried this, using cheap injection moulded plastics and marketing. WP used to have a lot more on Bose, but it was deleted during one of the religious wars. So it goes.
 * A bass speaker will still have to be large though.
 * Headphones are a little different. The frequency response of eardrums are themselves limited, so much of the low frequency comes from bone conduction. This allows headphones to achieve a useful bass performance, despite the limits of their small drivers. Andy Dingley (talk) 19:15, 15 October 2016 (UTC)
 * Wait, unobtainium is a term? I routinely use (the French version of) unfoundablium, and thought I was pretty witty to be the first to come up with the term. Tigraan Click here to contact me 17:48, 16 October 2016 (UTC)


 * It was the goal in the sci-fi Avatar (2009 film). StuRat (talk) 22:51, 16 October 2016 (UTC)


 * "Unobtainium, n. A substance having the exact high test properties required for a piece of hardware or other item of use, but not obtainable either because it theoretically cannot exist or because technology is insufficiently advanced to produce it. Humorous or ironical." -- Interim Glossary, Aero-Space Terms, 1958, Air University of the US Air Force. --Guy Macon (talk) 00:32, 17 October 2016 (UTC)

Blood tests
When you look at your blood test results, which is the specific blood test that would indicate concerns for high cholesterol? Which is the specific blood test that would indicate concerns for diabetes? And are these specific tests usually included in the CBC (Complete Blood Count)? Or are they ordered specially and individually? Thanks. Joseph A. Spadaro (talk) 19:19, 15 October 2016 (UTC)
 * Cholesterol is tested using a Lipid profile. Diabetes is tested for by using Glycated hemoglobin levels.  Neither is included in a Complete blood count, and will be requested specifically.  Of course, to discuss the results of a particular blood test, or if you're worried about your health, you should consult an appropriate professional. Tevildo (talk) 19:49, 15 October 2016 (UTC)
 * At least in the U.S., they generally only order a glycated hemoglobin test if you have elevated glucose levels. Glucose level is part of the basic metabolic panel, which in turn seems to be part of the standard tests most doctors order. To the original poster, if you are having tests ordered for yourself, your doctor or other practitioner will probably answer any questions you might have. --47.138.165.200 (talk) 03:52, 16 October 2016 (UTC)

Thanks. I have had many CBC's in the past. I wanted to know if I would find anything in there. I guess the answer is "no", then? Joseph A. Spadaro (talk) 15:04, 16 October 2016 (UTC)
 * We do have an article on the complete blood count. The CBC contains tests about hematologic parameters—the cells in the blood, including red blood cells, white blood cells, and platelets, and reveals information about their number and morphology. It doesn't include tests of blood chemistry, like glucose or cholesterol.
 * It's fairly standard screening in the U.S. for an initial evaluation of a patient to include both a CBC and tests of blood chemistry. Though they are thus often ordered at the same time (under the theory of "we have to draw his blood anyway, why not get two tubes in one stick instead of doing them separately") they test different things. - Nunh-huh 20:31, 16 October 2016 (UTC)


 * Yes, thanks. I had assumed that a CBC was more encompassing than it apparently is.  In my mind, the term "Complete Blood Count" always translated as "the generic blood tests that a doctor always orders about the most basic items".   I guess I was wrong about that.   Joseph A. Spadaro (talk) 03:14, 17 October 2016 (UTC)

Thanks, all. Joseph A. Spadaro (talk) 03:07, 20 October 2016 (UTC)

How do you *spill* methyl mercaptan?
The L.A. Times just published an enraging story about a community (Eight Mile, Alabama) reported to have endured 8 years of stench affecting 1300 people from 500 gallons of spilled methyl mercaptan.

What's confusing me is that methyl mercaptan is a gas sold in pressurized cylinders. How do you spill it, and why didn't it rapidly volatilize?

This is somewhat interesting since I see that a cylinder of methyl mercaptan seems to go for $200-$300, so for $10,000 a person could have fifty of them and (perhaps) build a "dirty bomb" that apparently can leave an entire community seeking long term evacuation. Wnt (talk) 20:31, 15 October 2016 (UTC)
 * Under pressure higher boiling point gases will liquefy. When spilt as a liquid, it would boil and cool down more. Perhaps there are also traces of less volatile mercaptans contaminating the original gas. These could stay around longer. Also methyl mercaptan could have reacted with ambient substances to make other longer lasting smelly sulfur compounds. One cylinder would disrupt a shopping centre but we don't want too many WP:BEANS.Graeme Bartlett (talk) 20:51, 15 October 2016 (UTC)
 * Also after reading the article, it claims to be in ground water. It could be stored underground for quite a while. Bacteria should be able to dispose of it if they can get oxygen. Face masks as seen in the protest will do nothing to stop the odor. Graeme Bartlett (talk) 21:00, 15 October 2016 (UTC)
 * From the article Wnt linked, I found Mobile Gas' FAQ website, explaining that their investigation discovered a line used to carry odorant was damaged by lightning. So there was a continuous source of new chemical flowing through that line - and leaking - over a potentially long period of time.  The facts about total quantity and duration, it seems, are subject to some dispute - hence the scandalous story as reported by the Los Angeles Times' reporters.
 * The website of Mobile Gas links to the State of Alabama's document archive, which contains even more information on the history and facts of the incident as they are known to the state government.
 * To follow up on Wnt's other concerns: most sources conclude that methyl mercaptan isn't harmful in the very low doses that one normally expects to encounter - but this material safety data sheet published by Chevron Phillips does list toxicity hazards as part of the full safety information for the chemical. In sufficient quantities, this chemical - like almost any other - transgresses beyond nuisance to become a real hazard.  Once again, because there is some dispute about quantities and durations of exposure, the community and the company seem to disagree about whether the case in Eight Mile, Alabama, was a mere nuisance or a true health-hazard.
 * But the same is true of many hazards: if a malicious group wanted to create nuisance or hazard, they could do so with many hazardous items that are freely available in the United States. On the spectrum of things to worry about, I'd say methyl mercaptan "dirty bombs" are low on the priorities list.  Emergency responders would probably be able to handle such an event by following "normal" HAZMAT emergency procedures.  I'm inclined to link again to caltrops - if an anarchic and malicious person wanted to harm a community, they could do tremendous damage using only a few dollars of parts and no special skills; this doesn't diminish the threat of "unique" chemical attacks, but it does demonstrate that difficulty-of-execution is not the primary barrier that prevents such antisocial behavior.
 * Nimur (talk) 20:54, 15 October 2016 (UTC)
 * Thanks for pointing out that link! I should feel guilty for not checking that link when I read the article, but I think the author should feel more guilty for not checking it when she wrote the article.  It says "Mobile Gas purchases its mercaptan from a vendor whose product contains a combination of tert-Butyl mercaptan and Methyl ethyl sulfide."  I still have to look these up, but tert-butyl sounds heavy and more liquid and stickier.... yeah, we have an article!  The methyl boils at 6 C, but the tert-butyl boils at 62-65 C.  So indeed it can be spilled as a liquid and can take much longer to evaporate.  I see prices as low as allegedly $600 a metric ton, if I believe Alibaba -- then again, I'm not sure I believe anyone here.  I mean, the simplest answer to the riddle of the stench is that somebody is lying about how much was leaked out of that line by several orders of magnitude... Wnt (talk) 03:21, 16 October 2016 (UTC)
 * The same way you spill helium: Really fast. Sagittarian Milky Way (talk) 03:43, 16 October 2016 (UTC)


 * To support Nimur's point mentions cleanup of an accidental spill using soapy potassium permanganate soloution. It doesn't mention it lasting long term after that. Of course intentional contamination over a wide area may be more difficult. Still I'm not sure if the Eight Mile case is a good example since it sounds like there has been a lot of controversy over precisely what has happened and what's been done . Note also that our Stink bomb article mentions US and Israeli law enforcement agencies and militaries developing devices for riot control and area denial weapons. It seems un likely that they don't have a fair idea of the capabilities of weapons using these and far more hard to obtain chemicals. Perhaps Butyl isocyanide (admittedly also a fairly toxic compound) which is available here  but only in lab quantities. (But I haven't looked at industrial chemical suppliers.) The first source quotes a 1937 experience:
 * "Butyl isocyanide proved to be so disagreeable to manipulate that none of its physical constants except boiling point were determined. Even when a hood with an extra forced draft was used, the odor pervaded the laboratory and adjoining rooms, deadening the sense of smell and producing in the operator, and in others, severe headaches and nausea which usually persisted for several days."


 * Nil Einne (talk) 07:05, 16 October 2016 (UTC)
 * Selenium and tellurium compounds might give these a run for the money, taking advantage of the periodically increasing stink down group VIB. Double sharp (talk) 07:41, 16 October 2016 (UTC)
 * A chemist of my acquaintance was contracted to make the flavouring for spring onion flavour crisps (scallion flavor potato chips). After making a batch he reported to his boss that it was a simple enough synthesis, and would generally have been worthwhile as a product. However the risk wasn't worth it - the chemical is such a powerful smell (like mercaptans) that if they'd ever spilled any, the clean-up would have been so difficult that it would have overwhelmed any profit they might ever have made from it. Andy Dingley (talk) 09:03, 16 October 2016 (UTC)