Wikipedia:Reference desk/Archives/Science/2012 February 22

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

February 22

Waterworld planet?

according to this]. The temperature of this planet is really high then how come there are a bunch of water? Isn't water just going to boiling up and disappeared all?Pendragon5 (talk) 01:30, 22 February 2012 (UTC)

Jean's escape equation defines the time-constant for atmospheric evaporation. The more massive the planet, and the smaller its radius, and the colder its atmospheric temperature, the longer it takes for the gas molecules to escape into space. If astronomers discover an atmosphere that appears to be out of place or "unstable" - in other words, the equation predicts that the gas should have evaporated by now - then something neat is happening! Perhaps water is being produced on the surface by geochemical processes. Perhaps life-forms are producing the water! The results of this new exoplanet, GJ 1214 b, have only just been made public, so it's probably going to be some time for planetary scientists to figure out what's really going on. The thing that boggles my mind is that a solar system can exist whose planets have a 2-day orbital period! What a strange star. Around our sun, that orbital period to place the planet awfully close to the solar chromosphere... You can read all about this star and its solar system in our article, GJ 1214. Nimur (talk) 02:21, 22 February 2012 (UTC)

Holy cow, that's mean something else is going on that we can't quite explain yet with our knowledge. Yea you're right, i believe there are infinite combinations of anything in the universe. So there may be some kind of chemical reactions that is going on in the planet that keep the water from boiling even with high temperature. Scientists have already made standard what for kind of environment is fit for life form but our standard may not be the same as somewhere else in the universe. Just because we haven't encounter the life form lives in extremely condition (a condition where most scientists would think that life organism is not possible). I even have weirder thought. We deem to think if there is life form then there must be water. No water = no life form. But well due to the infinite amount of combination perhaps somewhere in the universe that some organisms live of from fire, plasma, electricity...? And even developed into advanced civilization like us. And our earth condition would not be tolerable to them as their environment won't tolerable to us. Pendragon5 (talk) 04:46, 22 February 2012 (UTC)

The atmosphere is probably mostly steam. Lower down, where pressure is higher, liquid water may exist above the normal boiling point. Even weirder, as that article says, there could be "hot ice". Many of the gas giants in our solar system have a similar situation, but with methane in gas, liquid, and/or solid forms (even though it's almost all gas here on Earth). StuRat (talk) 04:53, 22 February 2012 (UTC)

Is there any evidence apart from the density that this is made from water? Perhaps it is largely oxygen, with solid oxygen core, or alternately it could be a nitrogen planet, or even neon, which should be a common element, or may be a carbon dioxide ball, like Venus almost is. Graeme Bartlett (talk) 11:11, 22 February 2012 (UTC)

Of course, any ordinary exoplanet specialist reads the pop-sci press release and mutters to themselves, "the press is going nuts over indirect observation! Why can't they contain that enthusiasm and just wait (five or six years) for the direct atmospheric spectroscopy results!" This exoplanet and its solar system have unique and fortunate geometry. The plane of orbit of the planet is approximately aligned with the direct radial line-of-sight to Earth. The proximity of the planet to its sun means that the planet's orbital period is very short, something like 40 hours. So, the planet occults its sun, as viewed from Earth, almost every other day! (Actually, it's more complicated, compounded by geometry and of course always limited by funding for shared space-telescope time; in the original paper, A super-Earth transiting a nearby low-mass star, the authors report four transit observations, spaced over about two months, spaced approximately 16, 3, and 16 days apart). Amazingly, those observations were conducted using eight 400mm telescopes - only slightly larger than my amateur-hobbyist equipment! These transit observations will continue to be observable from Earth. This will allow direct spectroscopic measurement of the planet's atmosphere, but that sort of work will almost certainly require space-telescope time. There are huge engineering hurdles to overcome, essentially because the signal is so weak. Nonetheless, astronomers and exoplanetary experts have an immense toolkit for pulling very periodic, very weak signals out of the noise. Indubitably, this specific solar-system was sought out because it satisfies the requirements for rapid and repeatable planet/sun occlusion observations. No doubt, direct spectral measurements of the atmosphere are the goal of the ongoing research. In fact, in the original discovery announcement, even the abstract states this goal quite clearly: "The atmosphere is probably escaping hydrodynamically, indicating that it has undergone sig- nificant evolution during its history. The star is small and only 13 parsecs away, so the planetary atmosphere is amenable to study with current observatories." Nimur (talk) 19:48, 22 February 2012 (UTC)

In our own system, Venus lost its water through a combination of high temperature and relatively weak gravity. But a much more massive planet has a higher escape velocity. See Atmospheric escape - there is a relatively simple mathematical relation between the escape velocity and the mass of the individual gas molecule which can reach it and fly out into space. Water is below that threshold on super-Earths; even hydrogen is below that threshold on gas giants. Wnt (talk) 15:57, 22 February 2012 (UTC)

I think that water itself could not escape even from (present-day) Venus - water's molecular mass is not much below that of N2, which is still abundant in Venus' atmosphere. But water is split into hydrogen and oxygen due to solar radiation, and that hydrogen can escape. --Roentgenium111 (talk) 22:59, 25 February 2012 (UTC)

Oxidation of Cyclohexanol to Cyclohexanone

Hello. I would like to synthesize cyclohexanone from cyclohexanol by oxidation with sodium hypochlorite serving as an oxidizing agent and acetic acid acting as a catalyst. Prior to workup, why must I neutralize the reaction mix? Thanks in advance. --Mayfare (talk) 05:31, 22 February 2012 (UTC)

"Because the procedures tell you to"? As you learned from answers to your question a few days ago, your lab procedures are all about separating the product from...everything else. No seriously, somehow you have to separate the product from the whole reaction-mixture mess (solvents, reactants, byproducts, decomposition products). Sometimes it's easy because the product has some noticeably different property (solubility, boiling point, etc.) than all that other stuff. Sometimes some certain components of the "other stuff" are too similar to the product to be easily separable from it. And sometimes there are chemicals in there that would create a certain hazard if they were subjected to the separation process. So the solution (ha!) is to convert the "too similar" or "could be hazardous" material into something more easily separable or safer to manipulate. DMacks (talk) 07:06, 22 February 2012 (UTC)

The answer here depends on your "workup". But I notice that acetic acid is miscible not only with water, but with chloroform and hexane, according to the article. Salts, on the other hand, don't tend to get along too well with those two. Wnt (talk) 18:48, 22 February 2012 (UTC)

Kalate or potassate

1. If KO⁻
   was a legitimate ion, what would it be called; likewise, what would NaO⁻
   be called - natrate, or sodate?
2. Why is HgO⁻
   called mercurate and not hydrargyrate?

Plasmic Physics (talk) 09:16, 22 February 2012 (UTC)

1. IUPAC says potassate[1]
2. hydrargyrate seems to be only used in dictionaries and not by people who want to write about the topic. IUPAC says mercurate. Graeme Bartlett (talk) 10:40, 22 February 2012 (UTC)

KO⁻ would really be an a pair of ions, K⁺ and O²⁻. It's potassium oxide, K₂O, with one K⁺ missing. Same for NaO⁻. Calling these ions potassate or natrate is misleading because it's implying covalent metal-oxygen bonding, and that MOH (i.e. KOH or NaOH) are acids.

Alkalide might be of interest. It seems both types of name (sodide/natride and potasside/kalide) in use. --Ben (talk) 10:50, 22 February 2012 (UTC)

Thank you. Of course, I was speaking hypothetically. The reason for me asking is that I'm working on a personal categorisation project that requires a universal nomenclature system. I devised one that is heavily IUPAC based, but applied to a more general sense - I am applying substitutiveorganic nomenclature to all compounds, while excluding special names like alkanoic acids. The categorisation tree is based on molecular structure, have a look if you want, but please don't make edits - User:Plasmic Physics/Aldehydes. A result of this, is parent hydrides of inorganic substances require new names, sodium hydride becomes sodane, hence, sodium hydroxide becomes oxidanylsodane. Earlier, I mentioned excluding special names like alkanoic acids, this means that names like propanoic acid becomes 1-oxidanyl-1-oxidanylidenepropane. For the time being, I'm avoiding cyclic compounds, I have not yet composed a funtional prioritisation system for them. Plasmic Physics (talk) 11:40, 22 February 2012 (UTC)

OK. Why invent a new system of nomenclature when several already exist? Is it because none so far are universal? --Ben (talk) 14:23, 22 February 2012 (UTC)

Yes, this new universal system is simply to make categorisation easier, by being able to more closely compare structurally similiar compounds.

do lobsters use their claws

do lobsters use their claws- --80.99.254.208 (talk) 09:18, 22 February 2012 (UTC)

Is this a serious question? Plasmic Physics (talk) 09:34, 22 February 2012 (UTC)

Yes. I don't know how I can make my question clearer :/ --80.99.254.208 (talk) 10:33, 22 February 2012 (UTC)

Yes. Graeme Bartlett (talk) 11:06, 22 February 2012 (UTC)

Except for lobsters that don't have claws, such as the sculptured slipper lobster (Parribacus antarcticus, Lund, 1793). The article for that beastie needs a reliable reference that it is fished commercially, even if as by-catch, and the biography for the zoologist is woefully lacking in text and supporting references. Just thought I'd mention this.--Shirt58 (talk) 11:17, 22 February 2012 (UTC)

I think it is a corrolary to natural selection / survival of the fittest, that if they didn't need to use their claws, they would have lost them, instead of wasting metabolic load growing them. In any case, I can tell you that if you grab one from behind, they try to reach back and grab you, same as a crab will. And if they can't reach, they'll reach out and try to nip the person in front. Wickwack124.182.22.17 (talk) 12:28, 22 February 2012 (UTC)

Perhaps the intended question was "What do lobsters use their claws for?" (I went to lobster and searched for claw but didn't see anything specific about their uses.) RJFJR (talk) 14:28, 22 February 2012 (UTC)

Lobsters use their claws for crushing and breaking open prey [2]. They are purely weaponry, lobsters are apparently unable to use their claws to pass food to their mouths due to their great size. The OPs question was not in the least bit foolish; there seems to be an element of sexual selection in the great size of the male crusher claw [3] and it is perfectly possible that the answer could have been that the claws were entirely for display. SpinningSpark 15:12, 22 February 2012 (UTC)

Agreed. Another possibility is non-functional "claws" that are just to scare off would-be predators. Or, they could be vestigial claws which no longer serve a function, but have not yet evolved away. So, while lobsters do use their claws, the question was entirely reasonable. StuRat (talk) 18:23, 22 February 2012 (UTC)

In the front of every Red Lobster restaurant is a tank containing live lobsters. There are always bands around their claws. So whether they actually use those claws or not, someone certainly thinks they do - probably someone with bitter experience. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:17, 24 February 2012 (UTC)

question

what is the meaning of t in eriochrome black t indicator115.184.178.226 (talk) 16:06, 22 February 2012 (UTC)

We have an article Eriochrome Black T but it does not answer the question. One could also ask why an indicator that changes from red to blue is named "black". Many other titration indicators seem to have equally puzzling names Fast Sulphon Black F, Naphthol Green B etc. SpinningSpark 18:05, 22 February 2012 (UTC)

The general question is addressed in Klaus Hunger, Industrial Dyes, Wiley-VCH, 2003:^[4]

"The commercial names of dyes are usually made up of three parts. The first is a trademark used by the particular manufacturer to designate both the manufacturer and the class of dye, the second is the color, and the third is a series of letters and numbers used as a code by the manufacturer to define more precisely the hue and also to indicate important properties of the dye. The code letters used by different manufacturers are not standardized. The most common letters used to designate hue are R for reddish, B for bluish, and G for greenish shades. Some of the more important letters used to denote the dyeings and fastness properties of dyes are W for washfastness and E for exhaust dyes. For solvent and disperse dyes, the heatfastness of the dye is denoted by letters A, B, C, or D, A being the lowest level of heatfastness, and D the highest. In reactive dyes for cotton, M denotes a warm- (ca 40 °C) dyeing dye, and H a hot-dyeing (ca 80 °C) dye.

There are instances in which one manufacturer may designate a bluish red dye as Red 4B and another manufacturer uses Violet 2R for the same dye. To resolve such a problem the manufacturers’ pattern leaflets should be consulted."

However, "T" is conspicuously absent. So far I haven't found anything useful with the keywords like "pattern leaflet" and "code letter". Synonyms for the dye include "Acid chrome black ET; cacid chrome black ETN; chrome black PB; mordant black 11, monosodium salt; eriochrom black T; solochrome black T; solochrome black T; sunchromine black ET; superchrome black TS."^[5] "Eriochrome is a registered trademark of Ciba Specialty Chemicals Corp" but I'm not finding anything from them directly online. So far, I'm not hitting the target here. I should say as a wild guess that Eriochrome Black T is used for a "titrant", but I didn't find anything to back that up in a search and it's probably wrong. Wnt (talk) 15:18, 23 February 2012 (UTC)

My guess was "titrant" also but I held off posting a guess. Still puzzled by the "black" designation. It is blue in solution and the article says it is a dark red/brown powder. SpinningSpark 09:32, 26 February 2012 (UTC)

Peripheral nerve injury specialist

What is the specialist for peripheral nerve injury called? Is it a neurologist or maybe a traumatologist? --Broadside Perceptor (talk) 16:29, 22 February 2012 (UTC)

If the nerve injury was caused by trauma then a traumatologist may well be involved in the first instance but likely to refer the condition to a neurologist once the diagnosis has been made and a secondary treatment plan established. Richard Avery (talk) 19:06, 22 February 2012 (UTC)

Thanks.--Broadside Perceptor (talk) 22:23, 22 February 2012 (UTC)

'Timing' a Year

Could someone check the validity of this statement for me: Since a year is really 365 days + 6 hours long, if you started a stopwatch at noon on January first and stopped it when the Earth had finished one complete orbit, you would stop at 6PM on January 1st, correct? --CGPGrey (talk) 18:02, 22 February 2012 (UTC)

That would be true if a year was really 365 days + 6 hours long, but it's actually a bit less than that. Specifically, I believe you want the tropical year, which is around 365.24219647 days long. That's 365 days and 5.81271528 hours or 365 days, 5 hours and 48.7629168 minutes or approximately 365 days, 5 hours, 48 minutes and 45.775 seconds. StuRat (talk) 18:04, 22 February 2012 (UTC)

As StuRat notes, it really depends on your precise definition of a "complete orbit"/your frame of reference. For the time taken for the earth to complete an orbit of the sun, with respect to the fixed stars (i.e. an "outside" perspective) you use the sidereal year. It's only about 20 minutes longer than the tropical year, clocking in at 365 days, 6.153 hours. Regardless, 365.25 days is a good approximation for most purposes. See year for more definitions and more info. LukeSurl ^{t c} 18:24, 22 February 2012 (UTC)

And those are just averages, it varies very slightly from year to year because of gravitational perturbations from other bodies like Jupiter. So if you tried it just one year it should be different. And of course if you tried it this year it wouldn't work because there is a leap day.. Sagittarian Milky Way (talk) 18:33, 22 February 2012 (UTC)

Do you want to think about that last statement a bit, SMW :-) ? {The poster formerly known as 87.81.230.195} 90.197.66.188 (talk) 21:11, 22 February 2012 (UTC)

He correctly pointed out that the calendar year is 366 days long in 2012. The sidereal year, and the solar year, are both still approximately "365.25-ish" days long for the period starting on January 1, 2012, ending the following year after one (solar or sidereal year period) has elapsed. Nimur (talk) 23:03, 22 February 2012 (UTC)

Meaning that if you start at noon on January 1st 2012, you would end at ~6PM on December 31 2012, not at ~6PM on January 1st 2013. 98.248.42.252 (talk) 04:29, 23 February 2012 (UTC)

Mechanical and electronic time pieces (used by the likes of you and me), (so forget about atomic clocks) record the passing of 'mean solar time'(an average) . That means that every 24 hours it is about 4 minutes out from the Siderireal day annual shift that makes up the quarter day and so compensates for this difference. Hence, after a year a watch 'should' if it be a perfect time keeper, show midnight at exactly midnight at the new year; not 6 pm or am or any other time. --Aspro (talk) 19:15, 24 February 2012 (UTC)

This is so wrong. The ~4 minutes over a course of a year sum up to 1 day, not a quarter day. A watch shows midnight at midnight, but that's not the question. The point is that if you start at midnight and wait a year then it won't be midnight because the ratio year/day is not an integer. 98.248.42.252 (talk) 04:34, 25 February 2012 (UTC)

Check the batteries in your slide rule. It has to be about a 'day' in total, otherwise the year would be 36 4 days. 23.93447 hr [sidereal day] x 365) = 8736.08155 hr which divided by 24 equals 364.003398. Hence the employment of Mean-Time. The quarter day is the difference between the two. But clock time is conterminous with the year midnight-to-midnight (which is the point of OP's question) . Unless of course, you can explain it better. I await you elucidation. --Aspro (talk) 20:25, 25 February 2012 (UTC)

1. I'm glad you did the math and now agree with me that ~4 minutes every 24 hours make up 1 day annually, and not a quarter day. Strangely you still claim that you can obtain a quarter day with some computation using sidereal day, but didn't explain how. 2. This diversion is irrelevant because the OP's question is about expressing the duration of a sidereal_year in days and hours. Doing so doesn't require the concept of a sidereal day. 98.248.42.252 (talk) 07:17, 26 February 2012 (UTC)

Five hundred twenty-five thousand six hundred minutes. LukeSurl ^{t c} 19:46, 26 February 2012 (UTC)

No hair theorem?

So an object appears to slow down so much that it can never appear to cross an event horizon, unless you have infinite time to wait or are yourself crossing the event horizon, right? How to reconcile this with the fact that black holes have no hair? If you have a one solar mass black hole formed 10 billion years ago and you just threw another solar mass in, shouldn't the newer mass be higher? When it's far away you can detect two masses, one of whom is very much not a black-hole. At infinite time (and not even because of Hawking radiation, but if that didn't exist) the same masses you were previously detecting is now only detectable as a single 2-solar mass object - which is most definately a black hole - with only the properties allowed by the theorem. How long are you allowed to detect non-allowable quantities of what you're throwing in before the no-hair theorem kicks in? Infinity minus a Planck time? Sagittarian Milky Way (talk) 18:25, 22 February 2012 (UTC)

Although you can't see an infalling object cross a black hole's event horizon (unless you're falling in, too), you don't just see it sitting there forever, either. Instead, it very quickly redshifts down to not being visible. Gravitational differences from a no-hair black hole also rapidly dissipate away at the speed of light, in the form of gravitational waves. Red Act (talk) 19:32, 22 February 2012 (UTC)

Hydrogenated Corn Syrup?

I bought some imported chewing gum from a local Japanese market. Like most imported food, it had an English language USDA style nutrition label glued on top of the Japanese nutrition label. The gum had the word "sugarfree" in English on the original packaging. But the English translated nutrition label noted the first ingredient was "hydrogenated corn syrup". I've never heard of hydrogenating corn syrup, or even why you'd want to do that. Or even if it's scientifically possible. So does it even exist? And what would be the advantage of using it? --76.79.70.18 (talk) 18:30, 22 February 2012 (UTC)

Corn syrup is not simply an extract of corn, but is produced by acid hydrolysis or amylase treatment of cornstarch. My first guess would be that the label means that, but of course catalytic hydrogenation is a different process used to produce partially hydrogenated vegetable oil and thus trans fats. I assume it's an error because cornstarch shouldn't have double bonds to saturate in this way. Wnt (talk) 18:40, 22 February 2012 (UTC)

It's almost certainly referring to Sugar alcohol. It's the carbonyl group that has been hydrogenated, rather than the olefin groups in a hydrogenated fat (For some reason, it's more common in chemistry to talk about reducing a carbonyl group, but hydrogenating a carbon-carbon double bond, despite them being chemically quite similar.) Buddy431 (talk) 18:59, 22 February 2012 (UTC)

Doh, I totally forgot about the acyclic aldehyde/ketone groups. Thanks for pointing that out! Checking for sources to be sure (what I should have done if I weren't being so ass-sure about the lack of double bonds), I get [6] "The product is produced by hydrogenation of corn syrup over a nickel catalyst.", [7] "The maltitol-containing mixture of sugar alcohols is suitably derived from a hydrogenated starch hydrolysate which is another name for hydrogenated corn syrup.", "Hydrogenated Corn Syrup, Technical Grade, is an aqueous solution containing about 70% total solids consisting of D-Sorbitol and other polyhydric alcohols. " etc. Wnt (talk) 19:10, 22 February 2012 (UTC)

I believe it's basically a synonym for High-fructose corn syrup, a common sugar substitute in the US and some other places. And re the second part of the question about the advantage of using it, well the article gives several reasons, but basically it all boils down to the only thing that matters - it's cheaper for the producers, meaning more sales and profits (and I guess as an added bonus you can somewhat deceptively advertise it as sugar-free). --jjron (talk) 14:16, 23 February 2012 (UTC)

Actually no, at least not according to these sources. Maltitol and sorbitol are indeed sugar alcohols, and hydrogenation over a nickel catalyst is different from the enzymatic conversion of glucose to fructose. Wnt (talk) 14:44, 23 February 2012 (UTC)

Sugar alcohols are often used as sugar substitutes for diabetics - they still have calories (unlike most artificial sweeteners), but they aren't digested so efficiently, so don't typically cause a spike in the glucose levels. Buddy431 (talk) 05:51, 24 February 2012 (UTC)

Interesting that a Google search for "Hydrogenated Corn Syrup" returns almost exclusively results for "High-fructose corn syrup". --jjron (talk) 07:35, 24 February 2012 (UTC)

Yeah, and the top hit is the Wikipedia article, which does not contain the word "hydrogenated". Someone was saying before that putting it in single quotes, putting a + in front of it and so forth would make a Google search work, but I keep getting that article with "+'hydrogenated' corn syrup. But trying an Advanced Search with scripts off and saying the exact word hydrogenated got me [8] which doesn't have it on top. I still don't get exactly what tells the Google search that yeah, you really, really, really, really want the search results to have the term you searched for in it. Wnt (talk) 19:16, 26 February 2012 (UTC)

Cooling speed

I was wondering: If I have a cup of hot coffee to which I intend to add cold milk from the refrigerator, and I'm going to leave the coffee alone for 10 minutes before I drink it, will the coffee be hotter in 10 minutes if I add the cold milk now, or if I add the cold milk in 10 minutes? Our article cooling is, disappointingly, a disambig page. I would have thought it would be great to discuss the subject of "cooling" at the cooling article. Our article section Thermal conduction#Fourier's law makes it pretty clear that, with respect to conduction, the answer is to add the cold milk now if I want the coffee to be hotter in ten minutes; but I can't tell whether the same guideline applies for the aspects of cooling by convection and radiation. Or how important each of the three methods of cooling is, in this case, relative to each other. (Hence my desire for a treatment of overall cooling at the cooling article.) Comet Tuttle (talk) 18:36, 22 February 2012 (UTC)

• I'll answer in terms of radiation: hotter if you added the cold milk now, as the rate of cooling is faster for when an object is at a hotter temperature. This is described in see Stefan–Boltzmann law (I'm assuming adding the milk won't change the radiative properties of the drink significantly). I'd imagine convection would be the same, though I don't know the process that governs this. LukeSurl ^{t c} 19:25, 22 February 2012 (UTC)

Yes, all modes of heat transfer are more efficient when a larger temperature difference exists. So, to make the coffee cool down the most, let in cool black, then add milk straight from the fridge. However, if you have to take the milk out of the fridge at the start, then the cold milk will also be warming up while we wait to add it, which complicates things. StuRat (talk) 21:22, 22 February 2012 (UTC)

We've answered this question many times before! We saw it in 2009 and 2008. It's been answered so often, I even wrote the Official Science Reference Desk Coffee-And-Milk Simulator, and provided source-code for it! (Unfortunately my web-server is no longer operating the web-based coffee-and-milk temperature graphing website, but if there's a strong desire, I can probably track that disk-image down and boot the computer up). Anyway, I wouldn't use the Stefan-Boltzmann law - while it is true that hot coffee does radiate heat, it's also transferring heat convectively. This is orders of magnitude more efficient at heat-transfer for normal coffee and ambient room temperatures; so we can basically neglect radiant heat loss during reasonable time-scales. This means you should probably use Newton's law of cooling as your starting-point physical model. Finally, the way the decaying exponentials math works out, you will always end up with a colder coffee if you add the milk sooner (contrary to some of the earlier answers posted); but there may be pathological confounding experimental factors; it's remotely plausible that convective turbulence or chemical changes could significantly affect the thermal properties, but this is pretty unlikely. Verify for yourself! Run the calculations! Try plugging my equations into the web-based Octave (or download GNU Octave for free to run on your own system)! Perform the experiments! Kitchen science is cheap and easy! Nimur (talk) 22:54, 22 February 2012 (UTC)

I'm still confused... I even remember seeing an episode of an Australian popular science show about this question when I was a kid and they came to the conclusion that adding milk later would result in colder coffee.. I think I'll need to run the experiment.. Vespine (talk) 23:42, 22 February 2012 (UTC)

After a quick look at this discussion, the 2009 dicussion, and the 2008 discussion, it is apparent that nobody has remembered evaporative cooling, nor followed two good principles: a) separate out the phases in the process, and b) put some numbers on it.

There are 2 phases: add the milk, and cool down.

Lets look at adding milk first: Typically, you would bring water to boil (373 K), then give it a short cool down to avoid "burning" the coffee. Water is now at (say) 370 K, and is (say) 90 ml. You'd keep the milk in the bottom row of the fridge, so it will be about 280 K. Add 10 Ml of milk to the water - equilibrium temperature is now (10*280 + 90*373) / 100 = 363.7 K. We now begin 10 mins cooling. Significant cooling is by TWO processes: convection of the sides of the cup (exponential decay toward ambient - say 298 K) and evaporative cooling of the top surface (also exponential decay toward 298 K) You can neglect radiation. Calculating this is a litle complex, we don't know cup surface roughness etc etc, so lets say temperature drops to x% (say 0.7) each 10 minutes. So the temperature ends up as 298 + (363.7 - 298)*0.7 = 348.4 K.

Now look at adding milk last. First, the cooling phase: after 10 minutes, temperature is 298 + (370 - 298)*0.7 = 348.4 K. Now add the milk: equilibrium is (10x280 + 90*348.4) / 100 = 341.6 K.

Conclusion: Adding milk first gives a higher end temperature (348.4 K vs 341.6 K) as the lower temperature during cooldown gives lower loss of energy. Ratbone60.230.199.35 (talk) 01:27, 23 February 2012 (UTC)

Evaporative cooling should also be more efficient with hotter coffee, just like every other cooling process, which means the milk should be added last, to cool it down the most, just as you, and most of us, have said. StuRat (talk) 02:02, 23 February 2012 (UTC)

It appears I have misspoke in my most recent comment. I can be wrong sometimes! I should have said, "you will always end up with a warmer coffee if you add the milk sooner." I apologize for the error. Nonetheless, the analysis was valid; this result is always true, regardless of the quantity of milk or the rate of cooling. StuRat is correct, though; you can roll evaporative cooling into the Newton's function, to first order. Nimur (talk) 02:14, 23 February 2012 (UTC)

It apears that Ratbone has assumed that when milk is added, it is stired in, as is done in England and Australia. If cream is added and left to float on the top, as some countries do, then heat lost via evaporation cooling will be prevented until the cream warms up. So, adding cream at the start will likely give you hotter coffee after the 10 min cooldown period, as only convection will be in full effect, whereas adding it last will allow convection AND evaporative cooling the whole time. It will depend a lot of the cup, but typically evap cooling will be more effective - styrofoam cups for instance will have enough thermal resistance to effectively prevent convection. You can use Pressman's empirical formula ( R = 7400 A^-0.7) where R is thermal resistance cup to ambient, A is area of cup outside exposed surface area), Rconvec in series with cup wall thermal resiatnce) to roughly estimate convection heat loss. I can't remember of hand how to calculate evap heat loss, but without cream, Ratbone is right, it will be significant. Wickwack121.221.99.50 (talk) 07:31, 23 February 2012 (UTC)

Well, the OP did say milk, which, unlike cream, will mix in all on it's own. StuRat (talk) 23:42, 24 February 2012 (UTC)

RIIIGHT! Ok, "warmer", now it makes perfect sense! :) Vespine (talk) 02:32, 23 February 2012 (UTC)

Thank you all for the thorough answers — but is there an article somewhere that discusses why radiation should be neglected in the analysis, and why convection affects the cooling much faster? Comet Tuttle (talk) 04:35, 23 February 2012 (UTC)

Not sure about an article, but radiation becomes more of a factor when you have thousands of degrees of temperature difference, especially if the other types of heat transfer are blocked, say by a vacuum. StuRat (talk) 05:59, 23 February 2012 (UTC)

asimov answer

This question was asked still another time:

http://wiki.riteme.site/wiki/Wikipedia:Reference_desk/Archives/Science/2008_March_30#add_milk_now_or_later.3F

Interestingly, one answer there said: "Isaac Asimov wrote that adding the milk early is the best choice if you want the coffee to be hotter later. Edison (talk) 20:21, 30 March 2008 (UTC)"

So we have quite an authority on this one... --80.99.254.208 (talk) 10:07, 23 February 2012 (UTC)

Concrete Resistant Materials

Hi all. I'm working on a project to design an apparatus to measure the setting time of concrete according to ASTM C 403. One of the components that's needed is a rigid container to hold the concrete during the testing and I'm trying to find some information on materials that are resistant to drying concrete to make clean up easier. I've tried Google, but I haven't found anything really applicable so any help you could give me would be appreciated. --Aces57 (talk) 19:49, 22 February 2012 (UTC)

Do a web search for concrete forms. I think most of these are made of wood and they are meant to be removed, so you can probably make your container out of wood. RudolfRed (talk) 20:22, 22 February 2012 (UTC)

Concrete forms are made of wood, metal or fiberglass and sprayed with a releasing agent, a light oil, to allow forms to be removed with a certain amount of hammering. Polyethylene/polythene doesn't stick well to concrete either and might be obtainable in an appropriate size fairly cheaply, depending on how rigid you need it to be, or can be placed in a rigid frame. Acroterion (talk) 20:27, 22 February 2012 (UTC)