Wikipedia:Reference desk/Archives/Science/2014 April 21

= April 21 =

Bazhin Gap
In the Nanga Parbat there is a high altitude gap/saddle called "Bazhin Gap". What does "Bazhin" refer to? Local dialect? A name of a person? The expression seems to be mentioned for the first time in the 1930ies. Any lead is appreciated.  GEEZER nil nisi bene 10:18, 21 April 2014 (UTC)
 * Probably a person. Note that there is also a "Bazhin Glacier" nearby. Looie496 (talk) 14:06, 21 April 2014 (UTC)

don't put warm food in fridge?
I had some leftovers that I was going to save in the fridge, but my mom says don't do that since they are still warm. I'm supposed to leave them on the counter til they reach room temperature before refrigerating. She says the same thing when we buy warm stuff from the store. What's the issue here? Does the quicker temperature change mess up the food in some way? Does putting the warm stuff (just an unfinished meal, not anything large) in the fridge temporarily warm up the fridge interior enough to speed the spoilage of other food in the fridge? Or is the whole thing just silly? Thanks. 98.207.66.10 (talk) 19:33, 21 April 2014 (UTC)


 * "Make sure food has cooled down before you put it in the fridge," says Philippa Hudson, senior lecturer in food safety at Bournemouth University.
 * "If the food is still hot it will raise the temperature in the fridge, which isn't safe as it can promote bacterial growth." 86.146.28.229 (talk) 20:09, 21 April 2014 (UTC)


 * See also Danger zone (food safety). If you place an overhot item in the fridge, you increase the chance of raising the temperature of all of the other food around it to temperatures that promote unhealthy bacterial growth.  -- Jayron  32  20:12, 21 April 2014 (UTC)


 * The U.S. Department of Agriculture says "Hot food can be placed directly in the refrigerator or it can be rapidly chilled in an ice or cold water bath before refrigerating." The U.S. Food and Drug Administration says "Leftovers … need to be refrigerated or frozen within two hours … . Despite what some people believe, putting hot food in the refrigerator doesn't harm the appliance."  The Washington State Department of Health labels the idea that you shouldn't put hot foods in the fridge a "myth", and says "Hot food can be placed in the refrigerator."  Red Act (talk) 20:24, 21 April 2014 (UTC)


 * I do wonder if there are climate and cultural differences. The stereotype is that Americans have larger, more powerful fridges than Britons: I know that I have watched the temperature in my fridge rise out of the safe zone, when I have overloaded it. And American food safety advice I have seen seems to assume a much warmer environment than British food safety advice: perhaps in line with the jokes about room temperature being laughably unrealistic in British labs. And every bit of American advice which claims it is a myth, that I have seen, also has a note about if you left the food to cool and forgot about it for hours, which perhaps shows the motive for the advice. This would explain why the official governmental advice from the NHS, supported by expert advice, is to allow food to cool before putting it in the fridge, whereas the official governmental advice in America is to not worry about that. 86.146.28.229 (talk) 20:31, 21 April 2014 (UTC)


 * I'd say it depends. If you have a powerful, almost empty fridge, containing food that doesn't really need refrigeration anyway (like fruit), and the food you want to put in isn't all that hot, but might tend to spoil quickly, then go for it.  On the other hand, if it's very hot, doesn't need refrigeration all that much, and you will need to cram it in right next to some foods that really need to be properly refrigerated (like egg salad), and your fridge can barely keep up with what's already in it, then wait. StuRat (talk) 22:57, 21 April 2014 (UTC)

Thanks, I see. At least this identifies the issue, of warm food in the fridge transferring heat to other food. Of course letting the warm food sit outside the fridge probably attracts even more bacteria, but whatever. 98.207.66.10 (talk) 01:09, 22 April 2014 (UTC)


 * This really depends on the food and circumstances. Soup in a pot with a lid that forms a seal can be brought to a boil and served, then left on the stove with the lid closed, be removed from heat, and let cool overnight.  As long as the lid is not removed and the stock was boiling it is sterile.  Leaving out uncovered eggs or dairy to cool is foolish.  Bacterial growth is normally most rapid around body temperature.  The worst thing to do is to let food sit warm.  It's an easy way to get you restaurant shut down.  Food should be under 40 or over 140F. If your fridge is from the 1940's a warm pot might be a problem, but letting a newer model run to cool the food is better than kidney failure. μηδείς (talk) 02:53, 22 April 2014 (UTC)


 * This thread reminds me of fan death. #science people. Putting something hot in the fridge will raise its temperature by .... how much?... versus the fact your food has been at incubating temperature for how much longer?... Actually come to think of it, this seems to be the approach most of europe takes to most problems, so I guess I'm not surprised. Shadowjams (talk) 07:26, 24 April 2014 (UTC)


 * ( Well you Americans with your giant powerful fridges would think that, wouldn't you? ) As Jayron, Stu Rat & Medeis say above, it depends on lots of variables, but I always follow the advice not to put very hot food in a small fridge.  It's just common sense.   D b f i r s   08:01, 24 April 2014 (UTC)


 * Fan death strikes me as a socially convenient belief. Obviously shutting off fans/air conditioners automatically saves money, energy, and removes unpleasant noise from the environment.  Yet for some reason it seems easier for some people to cite a different motivation. Wnt (talk) 01:14, 25 April 2014 (UTC)

Actually, newer model fridges may not be as good in dealing with this problem than older models. The newer models are a lot more energy efficient due to better insulation, but that means that the fridge doesn't run its engine as often as the older models. If you place a hot object in such a newer model fridge then the temperature in the neighborhood of the hot object will rise a lot more before the engine will run. If the engine only runs once every hour, then the heat from the hot object would have had to trigger the thermostat to run the engine, but that means that the stuff in the direct neighborhood of the object will have been heated well above the ideal temperature. In contrast, if you have an inefficient fridge that runs its engine every five minutes, then the heat from the object is irrelevant. There is then a large heat flux from the environment moving into the fridge that is almost constantly being pumped out.

What I do is I place hot objects in the freezing compartment of the fridge for about 15 minutes to cool them down to about 5 C (the time depends on the size of the object). The thermostat of the fridge reacts immediately to anything placed there and it's also well isolated from other stuff in the fridge (I don't use the freezing compartment of the fridge for storage at all). Count Iblis (talk) 17:20, 24 April 2014 (UTC)

Hypoxia
I have read the article on hypoxia, but it did not answer my questions. What are the cumulative effects of marginal hypoxia? What would the main symptoms be? Thank you. — Preceding unsigned comment added by 62.56.71.197 (talk) 21:45, 21 April 2014 (UTC)
 * I'm not an expert on hypoxia, but I suppose drowsiness and fatigue would be two of the most likely symptoms/effects. FWiW 24.5.122.13 (talk) 05:48, 22 April 2014 (UTC)


 * Confusion and muddled/slow thinking. It kills pilots because they are awake but unaware of danger or that help is in their interest.  --DHeyward (talk) 09:52, 23 April 2014 (UTC)


 * Kinda like getting really drunk on rum and Cokes -- you don't notice anything wrong until you're totally blasted. 24.5.122.13 (talk) 23:56, 23 April 2014 (UTC)
 * Cumulative effects of marginal hypoxia? There are no known cumulative effects. When a person receives sufficient oxygen that the blood is again fully oxygenated, the effects of any preceding hypoxia are completely erased. Dolphin  ( t ) 06:19, 25 April 2014 (UTC)

Rust treatment
Steel gasoline (UK: petrol) tanks of cars and motorcycles that have internal rust are difficult to clean, access is only via by small openings and most of the inner surface is out of sight. Vinegar which is mainly dilute Acetic acid is suggested in online videos as a rust remover so I experimented by letting the head of a rusty screw soak overnight in a teaspoonful of concentrated "Vinegar Essence 35%" which is cheap (and is probably safer than an industrial chemical such as phosphoric acid). The pictures show my results which are promising. The questions are:
 * 1) Surface rust on the screw has blossomed into a powdery scale (center pic). This happens above the submerged part of the screw. I suppose capillary action and/or a reaction in air occur. Can anyone explain what chemical reaction is likely here?
 * 2) The converted rust could be washed off with warm water (right pic). The bolt head is now almost rust free, and I can repeat the treatment. But in the case of a fuel tank I suspect the acid etched surface will be prone to rust again quickly. My question is what is a good way to finish the vinegar treatment? I am considering alternatives such as rinsing with Kerosene, Gasoline or with dilute caustic soda ?  JustAnotherUploader (talk) 23:50, 21 April 2014 (UTC)


 * I'm wondering if it makes economic sense to try to remove rust from a gas tank, instead of replacing it. To remove the rust you will have to remove the gas tank (which is quite a job, in the case of a car), drain it, then use quite a bit of whatever rust removing agent you decide on, then rinse that, then coat it with a large quantity of some type of anti-rust treatment, then maybe let it cure for a while, then rinse again, dry all the water out, then re-install.  The labor and other costs of all this sounds like it would exceed that of a new tank (or maybe a used one from a junkyard). Perhaps an exception might exist for old tanks for which no replacement can be found, or when you need to keep the original parts intact in a classic vehicle. StuRat (talk) 01:26, 22 April 2014 (UTC)


 * I have to agree with Stu. Have a professional replace the tank.  The last thing you need is rust particles flowing upstream into the engineworks. Pennywise, poundfoolish. μηδείς (talk) 02:40, 22 April 2014 (UTC)


 * Yes, I once had a vehicle that had rust in the fuel tank. I had to regularly remove the fuel injectors to clean them.    D b f i r s   16:51, 23 April 2014 (UTC)


 * If you need to do this because its a Classic vehicle its only worth doing properly. I used to own classic  cars,  so know,  that if you don't get all the corrosion off and the new surface properly sealed again the rust comes back real quick. Here's a link with photos. DIY Fuel-tank Rust Removal (by Electrolysis) & Rust Proofing Its a common task to do when renovating  old vintage bangers so there must be plenty more examples on the web.--Aspro (talk) 16:55, 23 April 2014 (UTC)