Wikipedia:Reference desk/Archives/Science/2014 January 30

= January 30 =

Standing water in my workshop not freezing at below 32 degrees
I live in detroit and my workshop as i measured today clocked in at around 24 degrees fahrenheit, but all of the standing water in cups and metal buckets that were there overnight were not ice. I do not think it has anything to do with pressure as detroit is slightly above sea level i think, and the decrease in pressure would seemingly effect the freezing point in the opposite direction, though maybe I am wrong.

I used an infrared laser temperature reader so i think the readings are pretty accurate, i measured the containers and the water itself and they were the same temperature.

The only other variable i can think of is that because the water was from the tap, that some minerals or chemicals are effecting the freezing point.

Any insight would be nice. 70.210.65.5 (talk) 00:23, 30 January 2014 (UTC)


 * That's not cold enough for water with salt or alcohol in it to freeze. Have you used either of those in your containers lately? InedibleHulk (talk) 01:42, 30 January 2014 (UTC)


 * Actually, according to that source, "Any foreign substance added to the water will cause a freezing point drop. For every mole of foreign particles dissolved in a kilogram of water, the freezing point goes down by roughly 1.8°C". InedibleHulk (talk) 01:44, 30 January 2014 (UTC)


 * There was no ice or alcohol in it, fresh water that was sitting in a metal pail, and a few in coffee cups. I guess my shop is pretty dusty so maybe the water is really full of dirt and stuff.

70.210.65.5 (talk) 01:49, 30 January 2014 (UTC)


 * I suggest you calibrate your temperature reader. Put some ice out in a plate, and wait for it to start melting.  At that point it will be 32 degrees F.  Measure its temperature, and see if you get a temperature below 32 degrees.  If so, the device is inaccurate. μηδείς (talk) 01:56, 30 January 2014 (UTC)


 * Could be some corrosion going on in the bucket, or in your pipes, little bits dissolving. 2 moles per kilo would be enough, and that's not a lot to see with your eyes. My tap water tastes coppery here and there. Maybe dust. Maybe a miscalibration. But rest assured, it's not black magic or some glitch of global warming. If it gets to -21 C (-5.8 F) and still acts up, then maybe call a priest. InedibleHulk (talk) 04:05, 30 January 2014 (UTC)


 * Water doesn't cool very fast when it's near freezing. I've been experimenting with time-lapse videos of water freezing, and it takes about eight hours for water in a soda can to start freezing from a temperature of 40F. --Carnildo (talk) 04:19, 30 January 2014 (UTC)


 * That's correct. Water has a high heat capacity and also a high Enthalpy of fusion, so a surprisingly large heat flow is needed to freeze your cups and buckets.  In the absence of significant airflow, freezing will take a long time.  I also suspect that the temperature of most of the workshop remained much higher, for most of the night, than your measurement in the early morning, so if rate of loss of heat was proportional to temperature difference, this would not be as large as one might expect. (Leaving the doors to your workshop open on a cold windy night will speed up the freezing process because convection carries away heat more quickly than radiation.)  It would be interesting to put a recording thermometer in your bucket to see how slowly the temperature falls.    D b f i r s   11:23, 30 January 2014 (UTC)


 * Infrared laser thermometers perform most accurately when directed at a matt black surface because the emissivity of the surface measure has a bearing on the measurement. You can improvise a matt black surface using a black marker pen on masking tape. Be sure to allow the tape to come into equilibrium with the object/environment. 78.148.110.69 (talk) 09:00, 30 January 2014 (UTC)


 * Still water also supercools before freezing on many occasions. shoy (reactions) 14:30, 30 January 2014 (UTC)

Delta Dagger, cont'd
As far as I know, the F-102 Delta Dagger had never seen actual combat in its intended role, which was that of a supersonic interceptor for use against bombers -- instead, it was employed in Vietnam as an escort fighter (unsuccessfully) and for ground attack (with surprising success). So, the only data that could indicate whether it would have performed well in its intended role comes from training combat exercises like the William Tell air-defense exercise (especially ones with live-firing of missiles); however, the article doesn't include this data, nor any links to it. Where can I find the data? (If you want to know, it's that "documentary" again -- what it asserts is that the Deuce was a piece of junk and a total waste of taxpayer money, whereas I'm trying to prove that it would have made a good interceptor, but it just wasn't designed for anything else.) 67.169.83.209 (talk) 02:01, 30 January 2014 (UTC)
 * I presume you're aware that those statements you make at the end aren't necessarily contradictory? Nil Einne (talk) 07:27, 30 January 2014 (UTC)
 * Will you PLEASE cut out the soapboxing and just tell me where I can find the training exercise stats (in particular, stats about the percentage of successful intercepts)? 67.169.83.209 (talk) 07:32, 30 January 2014 (UTC)


 * I found ANG Team Winners: Air Force Flying Competitions which only gives ANG winners and no other details. I also found SSP - In Action 199 - F-102A Delta Dagger but haven't found time to read through it. Alansplodge (talk) 17:20, 30 January 2014 (UTC)


 * Well, I've actually read the SSP booklet, but it doesn't have this particular info (although it does have a few stats about "Operation Stovepipe", which was that operation where they used the Deuce for ground attack). Guess these stats are harder to find than I thought.  Thanks for the effort anyway, and if anyone finds the interception %, please let me know! (BTW, I actually DO have the interception stats for the 6 Western Europe-based squadrons that used the Delta Dagger, but I need more comprehensive stats in order to be sure.) 67.169.83.209 (talk) 06:32, 31 January 2014 (UTC)
 * I presume you're aware you're the one who started with the soapboxing in your own question and I only pointed out, in small text, that your soapboxing didn't make much sense? I was never that interested in your question, but your reply pretty much assured I would not bother to look in to it. Nil Einne (talk) 15:23, 15 February 2014 (UTC)


 * The Dagger was used by the Argentine air force in the Falklands War (here's one apparently low over San Carlos Water attacking British shipping, and here's one apparently embedded in the Falklands Islands themselves). It seems from our article Argentine air forces in the Falklands War that somewhere between two and four Argentine squadrons used the Dagger in the war (I don't really know what an Air Brigade is). So this info is a major omission from the Operations section and the Operators section of the article about the Dagger. It doesn't help your question much, though, because the Argentines used the aircraft (almost?) entirely for air-to-ground missions. (The only Argentine air-to-air sortie I can think of was when some Argentine Mirages fired Matra missiles at Harriers, and missed.) --Demiurge1000 (talk) 01:14, 2 February 2014 (UTC)


 * Are you sure it was a Deuce, and not a Mirage? They both have the same basic design, so they're hard to tell apart in flight -- but the tail fin sure doesn't look like that of a Dagger! 67.169.83.209 (talk) 06:54, 2 February 2014 (UTC)
 * The Aircraft in the photo is either a Mirage III, or an IAI Nesher - an Israeli-built version of the Dassault Mirage 5. The Argentine Air Force renamed them Dagger after acquiring them from the Israelis. No connection to F-102. AndyTheGrump (talk) 07:06, 2 February 2014 (UTC)

Reusing turpentine substitute
I have some turpentine substitute that I used to clean Tip-ex (white-out/correction fluid) off some plastic templates. Previously having used this to clean paint brushes, the paint fell to the bottom after several days storage, allowing me to decant the liquid for re-use. In this case, it appears that some grey residue has formed in the bottom of the jar but the liquid remains white (light grey, really). Am I right in thinking this will never precipitate out? Perhaps I can just use the liquid in place of firestarters as accelerant for igniting wood in our chiminea? You're not meant to pour it into drains but since it's just a bunch of hydrocarbons, burning it shouldn't be more environmentally unfriendly than burning wood in a chiminea anyway, right? — Preceding unsigned comment added by 78.148.110.69 (talk) 08:35, 30 January 2014 (UTC)
 * No one here will take any responsibility for recommending any off-label usage of such stuff. You do what you gotta do, but realize that no one here told you it was a good idea. -- Jayron  32  15:15, 30 January 2014 (UTC)
 * First, we should establish that you are speaking, I presume, of white spirit / "mineral turpentine" etc. Our article is saying that that is a "light grade of kerosene" usable in stoves, though I didn't verify this.  Then there's our article on Tipp-Ex which says that the older formulation used until 2000 contained 1,1,1-trichloroethane.  I'm not confident to estimate the chance this could be volatilized in a wood stove to the point of becoming dangerous, though I'd think that its evaporation right after use would be the bigger problem.  My feeling though is that if this turpentine has been used and reused your biggest concern should be for other unknown/unspecified ingredients - lead paint for example.  See oil paint for a whole palette of possibilities.  (I'd tend to think that many of these compounds would have precipitated out in large degree, but I'm nowhere near ready to make a blanket guarantee!) Wnt (talk) 16:59, 30 January 2014 (UTC)
 * I regularly use old white spirit for lighting fires and have never had any problems, but we cannot make recommendations on health and safety except to say that, if you are go ahead, "use with care". I still have some 1,1,1-trichloroethane and can confirm that it evaporates very quickly (and even from a tightly closed container over time) so it is most unlikely that any trace will be left.  You could also use the liquid for a first-clean of future paint brushes.  The grey residue will probably precipitate out if left for a long time.  Be careful that it doesn't stain your chimenea.    D b f i r s   17:32, 30 January 2014 (UTC)

using ENCODE
to find or watch detailed sequences in a given genome (e.g., the human one) - how do I get to them ? It'll be of great help to get assisted here. BentzyCo (talk) 18:03, 30 January 2014 (UTC)
 * The article points you at the front door ( http://encodeproject.org/ENCODE/ ) which leads to more specific data with some exploration (e.g. http://encodeproject.org/cgi-bin/hgTracks?db=hg19&position=chr21%3A33031597-33041570 ). Given the systematic, top-down nature of the project I'm a bit surprised at the spottiness of the coverage of certain things at this point, but there's a vast amount of data there nonetheless.  To the best of my knowledge, the data still finds its way through to the universal repositories such as http://www.ncbi.nlm.nih.gov/ - see  for an overview of some of their capabilities. Wnt (talk) 18:58, 30 January 2014 (UTC)

Does a colder freezer make ice faster?
Just curious if reducing the temperature of a refrigerator's freezer compartment would make the built-in ice maker produce ice faster? --Navstar (talk) 20:41, 30 January 2014 (UTC)
 * Yes, of course. I don't have a specific ref for you.  But you might look at latent heat of freezing.  The greater the temperature differential, the faster heat flows out, and the sooner you've extracted the latent heat. --Trovatore (talk) 20:44, 30 January 2014 (UTC)
 * Oh, wait, you're talking about an icemaker. In that case I don't know.  If the icemaker is separate from the freezing compartment to the extent that the temperature in the latter doesn't affect the temperature in the former, then it wouldn't.  You'd have to provide the specific design. --Trovatore (talk) 20:46, 30 January 2014 (UTC)


 * Be careful!  While the obvious answer revolves around the fact that the rate of heat loss is proportional to the difference in temperature (Newton's law of cooling) - which naively appears to prove that a colder freezer would make ice faster - but it's not necessarily correct in this case.


 * Consider that ice is a much better insulator than water.  If you freeze the outer surface of the water quickly, the insulating ice layer will slow down the cooling of the remainder of the liquid.   On the other hand, if you chilled the entire body of water down to just a fraction of a degree above freezing, then brought the temperature down below freezing very quickly, then the entire ice cube can freeze almost simultaneously...and quite rapidly.  You can probably do even better by 'super-cooling' the water to below zero centigrade and then having it freeze in a fraction of a second!


 * So the answer isn't an obvious and unambiguous "yes!" - but the precise answer is rather nuanced and may well depend on the kind of material that the ice cube tray is made of - its volume, shape and thermal conductivity and so forth.


 * A classic example of how this kind of thing can be highly counter-intuitive is the Mpemba effect - in which (in certain circumstances) it's possible for warm water to freeze faster than cold water!  This seems entirely improbable - but it does seem to be true under certain circumstances.


 * I wouldn't be happy with giving an unambiguous answer to this question!


 * SteveBaker (talk) 21:24, 30 January 2014 (UTC)
 * OK, I see your point. There could be odd nonlinear effects.  I'm not so sure I buy the scenario in the second sentence of your second paragraph, though.  It's not all (or even mainly) about temperature; most of the heat is the latent heat of fusion.  I'm not sure why you wouldn't get the same insulating layer of ice when the already-cold water started to freeze, preventing you from extracting the latent heat from the water on the inside. --Trovatore (talk) 21:34, 30 January 2014 (UTC)


 * I've tried to replicate that Mpemba effect a few times. Tried and failed. Not to say it's impossible, but tricky. InedibleHulk (talk) 22:35, 30 January 2014 (UTC)


 * The simple answer is that the "Mpemba effect" is a pseudoscientific claim with neither factual evidence nor any coherently posited mechanism--per our own article. That said, Newton's a rather well-respected source, and if we're going by anecdote, we replicated his results with statistical significance in high school. μηδείς (talk) 22:38, 30 January 2014 (UTC)
 * Aye. I'm still a little partial to it, based on the time I chopped a log into three equal pieces with one swing. The old "something improbable was possible, therefore all improbabilities are probably possible" logic. Doesn't work, but it might. InedibleHulk (talk) 01:08, 31 January 2014 (UTC)
 * I would guess that most fridges with built-in ice maker have only a single cooling circuit, in which case a cooler fridge would imply a cooler ice-maker. Steve's technically correct but practically probably irrelevant comment withstanding, I would expect this to produce ice faster. --Stephan Schulz (talk) 21:43, 31 January 2014 (UTC)