Wikipedia:Reference desk/Archives/Science/2012 April 11

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April 11

why phenolphthalein instead of bromocresol blue

In the titration between NaOH and HCl to determine the end point. Is it just because phenolphthalein turns purple at approximately pH 7, whereas bromocresol green turns blue at pH much less than that? — Preceding unsigned comment added by 150.203.114.37 (talk) 04:19, 11 April 2012 (UTC)

See pH indicator, especially the big chart. Phenolphthalein doesn't hit the mark very well; you'd usually want to choose an indicator whose transition changes at the equivalence point of the titration, and phenolphthalein does so at much to high a pH. So, hypothetically, your reasoning would work, except that at pH 7, phenolphthalein hasn't changed color yet. However, for a titration like this, the equivalence point happens fast; one drop will generally get you from a very low pH to a very high pH, basically within one drop you go from pH 2 to pH 12 or something like that. Since you can't actually hit the mark that close, phenolphthalein has the advantage of being cheap and easier to work with than more vibrantly-colored indicators, which tend to stain your clothes and/or skin when you spill them. It is a good general purpose indicator for any titration with sodium hydroxide as the titrant, since your equivalence point will always end up sending you to a high pH really fast. --Jayron32 04:39, 11 April 2012 (UTC)

If the standard acid or base is so concentrated that one drop changes the pH from 2 to 12 as you say, couldn't you use a weaker solution of the titrant? (Its been a while since I took a chem lab). Edison (talk) 15:33, 11 April 2012 (UTC)

It's not that the titrant is too concentrated, it's that titrating a strong acid with a strong base results in a very weakly buffered solution (water is effectively the buffer, and it does a crappy job of it). A shift in pH from 2 to 12 is a bit of an exaggeration, but a swing of four or five pH units with a single drop isn't unreasonable. (Going from pH 5 to pH 9, for instance, means shifting from an excess of just 10 μM of acid to an excess of just 10 μM of base.) TenOfAllTrades(talk) 16:49, 11 April 2012 (UTC)

There's not really much of an advantage to getting finer resolution anyway if all you want to do is determine the eqivalence point. The equivalence point is the where the change is most rapid, so if with 1 drop the pH went from say 5 to 9 then you know where the eqivalence point was in terms of titrant to a pretty good certainty. 110.151.252.240 (talk) 18:26, 11 April 2012 (UTC)

The powder coating process

Hello,

The "The powder coating process" is a very informative article. Thank you.

Now to a question - In the "Part preparation processes and equipment", The second and third paragraphs talk about chemical pre-treatment, and the fourth paragraph begins "Another method ------. I'm a bit confused. From the article I'm led to believe that either one does the chemical pre-treatment before applying the powder, OR one uses abrasive blasting but not both.

From readings that I have done as well as speaking with applicators it seems one first uses an abrasive blasting procedure and then one can ALSO use a chemical treatment (phosphating) for added pretreatment before applying the powder.

By the way, I am having a mild steel railing fabricated, and then want to have an applicator apply a textured polyester-TGIC powder.

Your thoughts and clarifications would be most appreciated.

Richard Krause — Preceding unsigned comment added by 173.79.200.227 (talk) 16:12, 11 April 2012 (UTC)

For others' reference, the article Richard is talking about is powder coating. -- Finlay McWalterჷTalk 16:17, 11 April 2012 (UTC)

It's either or both, depending on the surface and powder composition. What if you had a surface which required a treatment but was covered in rust? You would want to blast it then treat it. 71.215.74.243 (talk) 23:14, 11 April 2012 (UTC)

Impossible colors

The CIE 1931 color space chromaticity diagram.

The article impossible colors says that we cannot in normal circumstances perceive a color red-green that is similar to both red and green. Indeed, the CIE 1931 color space chromaticity diagram shows that a combination of a pure red hue and a pure green hue (on a line between them in the diagram) will be perceived as yellow or orange. But suppose we fill a screen with intermingled red and green squares. If the squares are very large, the viewer would be aware of seeing the two colors separately and simultaneously. And presumably if the squares are extremely small, the viewer would see yellow (or orange).

Question: If we start from very large squares and then gradually diminish their size, is there a size that results in the viewer perceiving reddish green? That is, do the large red and green squares appear to merge into something reddish green, or does the perception jump from separate reds and greens directly to yellow/orange? Duoduoduo (talk) 17:02, 11 April 2012 (UTC)

The latter. I agree that yellow does seem to be a different color altogether, versus cyan, which looks like blue-green, and purple, which looks like red-blue. I wonder why. StuRat (talk) 19:53, 11 April 2012 (UTC)

Some WP:OR: I created a large yellow square in Microsoft Paint, and approached it gradually with a magnifying glass. The visual impression went from pure yellow to a pattern, that first looked like yellow vertical stripes on a black background, then like parallell red and green stripes with a black line in between (the blackness of course being the unlit blue pixel components). There was no reddish green at any point if I had the magnifying glass focussed. And if it was out of focus, the impression was yellow. --NorwegianBlue ^talk 20:52, 11 April 2012 (UTC)

Brown is also red plus green. 71.215.74.243 (talk) 05:17, 12 April 2012 (UTC)

See the articles Additive color and Subtractive color. When you are mixing paint (subtractive color mixing), your statement is true. When you are pointing a red light source and a green light source toward the same spot (additive color mixing), the result is yellow. --NorwegianBlue ^talk 06:17, 12 April 2012 (UTC)

Brown is more or less "dark yellow" anyway, so the two statements are not really incompatible. (OK, some brown is dark orange.) --Trovatore (talk) 06:20, 12 April 2012 (UTC)

Why don't they place neutron absorbants under nuclear reactor cores?

Couldn't that reduce the severity of nuclear accidents? Sagittarian Milky Way (talk) 17:06, 11 April 2012 (UTC)

That is too sensible and would cost extra money. A basin of cobalt or some such would suggest that the engineers are not confident in their design. Next, we would have airlines handing out parachutes to all their passengers before boarding. an' if they do start handing out parachutes, I want one of those military multicoloured types that can stand out whether I land in desert, jungle or downtown Harlem. Plus a good pistol and some of those tasty barley-sugar sweets -to keep me going until I get rescued. Oh, and of course a survival pack which includes an iPod would be de rigueur. --Aspro (talk) 17:56, 11 April 2012 (UTC)

Oh no! Someone used the words "airlines" and "pistol" in the same post! I suggest everyone assume the party escort submission position until DHS agents arrive to resolve the situation.Anonymous.translator (talk) 18:30, 11 April 2012 (UTC)

I think that untrained passengers jumping out of an airliner experiencing difficulties in mid flight would be orders of magnitude more risky than assuming the brace position and hoping that problem is resolved before impact (the engines restart, or they aircraft stops stalling, or whatver). And iPods would interfer with the aircraft's navigation systems (or so the hostesses keep telling me). And I told you...you don't get a gun until you tell me your name. 110.151.252.240 (talk) 18:39, 11 April 2012 (UTC)

If the core melted and a China Syndrome event began, wouldn't the molten mixture just go right through any neutron absorbant shield? 110.151.252.240 (talk) 18:33, 11 April 2012 (UTC)

No. Enough neuron absorber (say in a configuration of erect wedges) would stop the reaction and thus the heat generation.--Aspro (talk) 18:40, 11 April 2012 (UTC)

My general understanding is that, by the time you have a meltdown and a containment breach, the nuclear fuel is sufficiently dispersed so that the chain reaction is effectively finished. This suggestion, then, puts neutron moderators where it's too late for that particular property to be of any real use. Note also that, under these circumstances, neutron moderators won't be thermally significant, as heat generation will increasingly be from byproduct decay. Thermal protection is critically important, yes, but the history of nuclear incidents seems to bear out that bulk concrete is pretty good at the job. — Lomn 19:04, 11 April 2012 (UTC)

Poking around a bit more finds the relevant concept at core catcher, a portion of the plant engineered to catch and cool molten corium from a meltdown. — Lomn 19:15, 11 April 2012 (UTC)

This is my understanding as well. By the time you're burning through the floor, the heat is the issue, not the chain reactions. I also wonder whether vaporized radioactive cobalt would be a good idea to add to a catastrophic accident. I suspect not. --Mr.98 (talk) 19:17, 11 April 2012 (UTC)

(ec) Decay heat has a bit more on this. If you SCRAM a reactor that's been in operation for a while, there will be lots of radioisotopes present in addition to the original uranium; some of these isotopes have rather short half lives. If you shut down a normal reactor, the core will continue to output about 7% of its normal operating power due to ongoing decay of these isotopes. (This drops off over time, but it means that a reactor continues to need active cooling for days or weeks after shutdown.)

Late in a meltdown, there isn't a chain reaction to interrupt – the molten corium is probably mostly subcritical by the time it gets to the reactor floor – but the corium is still going to be making its own heat for hours, days, and weeks. As Lomn says, you just have to wait until the radioactive molten goo is mixed with enough cold metal, concrete, and rock to keep from melting any further. TenOfAllTrades(talk) 19:32, 11 April 2012 (UTC)

According to the article on the Chernobyl disaster, the chain reaction was effectively stopped about two or three seconds after the first explosion. The corium was still over 1600°C 4 days later, and it is still hotter than the ambient temperature right now. 110.151.252.240 (talk) 20:21, 11 April 2012 (UTC)

Reading uranium dioxide, why'd they choose that as the best nuclear fuel? It seems like a poor nuclear fuel to me. Is the uranium-compound and other fissile substance-list really that crappy that no suitable reactor fuel could be found with a melting point lower than 2865 °C, which would be easier to contain with structural materials if melted? Then you might be able to catch the stuff with a neutron-killing crucible/isolater. If not couldn't they have at least found a fuel with a higher thermal conductivity? It's use is to make heat for crying out loud, and one where hotspots are dangerous.

I wonder if they considered just allowing the molten fuel to mix with and melt some other material, like lead, beneath the reactor core, to both dilute and shield it. StuRat (talk) 22:11, 11 April 2012 (UTC)

The actual rods are a very complex mixture of the uranium dioxide fuel, compounds containing daughter isotopes and other materials. Having lower melting points is no advantage as far as I can see; if the fuel rods melted at a lower temperature then the reactors operating temperatures would be more constrained. Why do you think it's better to be able to catch molten fuel rods then to just keep them solid and have them not melt in the first place? And allowing the hot lava like melt to come into contact with lead is not a great idea either; lead boils at 1749°C so you'd have a radioactive mixture of very hot gaseous metals building up pressure inside whatever is left of your containment. This effect contributed to the disaster at Chernobyl but with zinc instead of lead coming into contact with the corium. 110.151.252.240 (talk) 22:23, 11 April 2012 (UTC)

I think the idea is that the rods will continue to heat up until they do melt, whatever than melting temp is, in a disaster like Chernobyl. So, if they are going to melt in any event, do we want that to happen at a lower or higher temp ? StuRat (talk) 22:28, 11 April 2012 (UTC)

Higher, so that they're not as volatile. 110.151.252.240 (talk) 22:33, 11 April 2012 (UTC)

Is something at it's melting point of 1000°C necessarily more volatile than something at it's melting point of 2000°C ? StuRat (talk) 22:56, 11 April 2012 (UTC)

No, but assuming we're still using some compound of uranium, the nuclear reactions are all still the same so the same amount of energy is released and heats the material by the same amount. So if it takes less heat to get to the melting point then there's more heat to push closer to the boiling point. Just doing some ball park maths the material in the Chernobyl incident could have boiled ~20 tonnes of lead (my assumptions were; that heat transfer from the corium to lead heat sink is uniform across the entire body, the corium mixture is at the melting point of uranium dioxide, that all of the corium has the heat capacity of uranium dioxide, the entire mass comes to thermal equillibrium at the boiling point of lead). 110.151.252.240 (talk) 23:06, 11 April 2012 (UTC)

The sooner it melts, and thus mixes with and melts the lead, the sooner the chain reaction with be slowed by the shielding. Yes, the total amount of heat released will be the same, but it will be released at a much slower and more manageable rate. StuRat (talk) 02:03, 12 April 2012 (UTC)

Apparently, there are reactor designs that use molten fuel, and these designs are inherently more stable that solid fuel types. I suppose it wouldn't be possible for them to melt down as such, though they could boil and leak or explode. It seems like cooling the molten salt would be much more straight forward though. 1.155.25.201 (talk) 05:02, 12 April 2012 (UTC)

When everything is working properly, yes, but we must assume that any system designed to circulate and cool the molten salt could be disabled. StuRat (talk) 17:35, 12 April 2012 (UTC)

Seems pointless to try to think of a way to do it better (well, unless you're a nuclear engineer) however I did read in the Economist that many designs are old as dirt but anything in the industry happens so dang slowly and expensively that they don't even bother. Sagittarian Milky Way (talk) 21:54, 11 April 2012 (UTC)

Use of anova/ F-tests with count data

Hi all. I've done some reading recently for a lit review (etc) and I keep coming across studies that use ANOVAs for discrete data. For example, someone gives experimental and control subjects the same 20 words of French to learn, then tests them after, say, 10 minutes, to see if there is any difference between the two groups. They almost always seem to use an Anova for this. The scores are discrete, so they can't really be from a normal distribution, can they? Kasahara (2011) is a case in point, as is Laufer and Shmueli (1997). Is this approach justified? Or is it because they don't know what they are doing, and because non-parametric statistics or robust statistics confuse people? IBE (talk) 19:47, 11 April 2012 (UTC)

Aggregations of discrete scores often form normal distributions. 71.215.74.243 (talk) 23:17, 11 April 2012 (UTC)

Actually an ANOVA would not properly be used in the situation you describe -- a simple count test would suffice. The proper use of an ANOVA is when there are multiple groups (more than two) and you want to see whether you can reject the hypothesis that all of the groups are statistically identical. I believe that's what is happening in those papers, but I don't have online access to them so can't be sure. There are many situations where counts are approximately normally distributed with high accuracy if the number of samples is large. Looie496 (talk) 00:16, 12 April 2012 (UTC)

You are right, people using ANOVA for discrete data don't know what they are doing! After observing k type-1 items in a sample of n items from a big population, the posterior probability P that a random item from the population is of type 1, has a beta distribution, P ≈ μ±σ, where the mean value is μ = (k+1)/(n+2) and the variance-to-mean ratio is σ²/μ = (n−k+1)/((n+2)(n+3)). The difference between two populations, P₂−P₁ ≈ μ₂−μ₁±√(σ₂²+σ₁²), is approximately normally distributed, and if actually P₂ = P₁ then the square of the normalized difference, (μ₂−μ₁)²/(σ₂²+σ₁²), has a chi squared distribution with one degree of freedom. Bo Jacoby (talk) 06:21, 12 April 2012 (UTC).

My father in law (now retired) held an academic position in the social sciences, and was an expert in doing ANOVAs on massive data sets by hand. I asked him about how he could be sure that his data fulfilled the requirements for doing an ANOVA. His answer was that he wasn't, but that it was common practice in his field, because the results gave meaningful and practically useful results. (This conversation took place at least 20 years ago). --NorwegianBlue ^talk 06:01, 12 April 2012 (UTC)

You can't derive a posterior distribution without a prior distribution. You seem to be assuming a prior distribution of binomial(n,0.5), but that isn't automatically a sensible choice. There are plenty of situations where 0.5 isn't a good prior and even when it is a good choice you should be explicit about what assumptions you are making. --Tango (talk) 19:12, 12 April 2012 (UTC)

When n=k=0 the beta distribution is the uniform distribution on the interval 0<P<1. So the prior is P = 0.5(3), rather than P = 0.5(0). (See Concise notation#Measurements). Bo Jacoby (talk) 11:19, 13 April 2012 (UTC).

• Thanks for the response, IBE (talk) 21:32, 15 April 2012 (UTC)

Magnesium citrate

While cleaning out my medicine cabinet I found an old bottle of magnesium citrate, oral solution, saline laxative, cherry flavor. Since it expired over 6 years ago and had a white crystaline precipitate at the bottom, I decided to dump it. I thought the precipitate was attached to the bottom, but, when I poured it down the drain it broke up and fell down the drain, where it's now lodged. My question is, do I need to fish it out, or is this precipitate water soluble, and will it eventually dissolve ?

Here are the ingredients:

Magnesium citrate, 1.745 g per fluid ounce
Cherry flavor
Citric acid
FD&C red #40 (I figure this can't be in the precipitate, since it's white) 
Potassium bicarbonate
Sodium saccharin
Purified water

I tasted a bit of the precipitate which didn't fall down the drain. It was sweet. So, I imagine this means there's some of the saccharin in it. StuRat (talk) 20:19, 11 April 2012 (UTC)

It might take a while to dissolve. Have you tried running hot water for 10-15 minutes? 71.215.74.243 (talk) 23:24, 11 April 2012 (UTC)

Magnesium citrate is very, very soluble - 20 g/100ml according to the article. But exposure to the air might (I think) have generated magnesium carbonate (from carbon dioxide in the air) which is only 0.01 g/100 ml. The fact that you're even asking makes me think you might have the carbonate, in which case, it may take some doing, but it should dissolve if you can keep the water flowing through it. Wnt (talk) 15:46, 12 April 2012 (UTC)

It seems to have now dissolved enough to fall down into the U-bend. Hopefully it will dissolve the rest down there. StuRat (talk) 16:20, 12 April 2012 (UTC)

Gauss' principle of least constraint

Apologies if this is a stupid question, but I haven't found any clear discussion on this matter.

I have read that Gauss' principle of least constraint is the most general variational principle of Classical mechanics, and more general than Newton's laws, but I still don't understand what this means. For the sake of convenience, take Newton's laws to say nothing other than that momentum is always conserved (I am aware of other interpretations, especially regarding the first law). I ask

1. Does Gauss' principle imply Newton's laws? By this I mean can Newton's laws be derived from Gauss' principle?
   1. If yes, what does Gauss' principle also say that Newton's laws do not?
   2. If no, is Gauss' principle a weaker statement, and if so, how is it weaker?
2. To what extent if there experimental data to support Gauss' principle in as much as it differs from Newton's laws?

Thanks.--Leon (talk) 20:23, 11 April 2012 (UTC)

Yes, Gauss' principle implies Newton's laws, and provides a way to solve for thermodynamic systems which Newton's laws do not. See [1]. To the extent that they make the same predictions, they are supported by the same empirical evidence. 71.215.74.243 (talk) 23:32, 11 April 2012 (UTC)

I've answered your questions in sequence:

"Does Gauss' principle imply Newton's laws?"

Yes; in fact, it is mathematically equivalent to the statement of Newton's laws, using a generalization of spatial coordinates. You can see a derivation of this in Marion and Thornton's Classical Mechanics text, (Chapters 7 through 9).

"If yes, what does Gauss' principle also say that Newton's laws do not?"

The use of generalized coordinates allows simpler algebra, permitting analytic solutions in cases where Newtonian formulations would require numerical computation. But to the letter, these equations are equivalent to Newtonian physics. They're just written in a different notation, which helps make certain relationships more clear and simpler to write and calculate.

"To what extent if there experimental data..."

This one is a bit tricky. In a sense, like Newton's laws, Gauss's statement is definitional - axiomatic - in that it contains a generalization of the physical quantity "force." Gauss's statement implies conservation of energy and conservation of momentum, and is in fact equivalent to a definition of energy and momentum and force, in terms of mass and generalized coordinates. Therefore, any experiment that validates energy- and momentum conservation is a validation of the principle of least-action. Nimur (talk) 00:14, 12 April 2012 (UTC)

I didn't realize that Gauss' principle or Newton's laws said anything about energy conservation; I thought that energy was simply the value of the Hamiltonian, which is conserved iff the Hamiltonian has no explicit time dependence. And I thought that Hamilton's principle was weaker than Newton's laws and Gauss' principle as Hamilton's principle requires holonomic constraints whilst the latter two do not. Where am I going wrong?

The article on D'Alembert's principle claims that no one has proven that it is equivalent to Newton's laws, and I thought that Gauss' principle was known to be equivalent to D'Alembert's principle. Where is the mistake?--Leon (talk) 09:44, 12 April 2012 (UTC)

Our article is incorrect. It cites a source, but the source is in German, which I don't read very well; I specifically recall a physics professor telling me I'd never be a real physicist until I learned to read German and blow my own glass, but despite some effort, I never spent enough time to master either art. Nonetheless, I still try to read as much work in its original language as possible. I can't begin to tell you how many misunderstandings about quantum physics perpetuate to this day because of poorly translated German. Anything you read in English involving gedankenexperiments, ansatz functions, Schrodinger's cat, or eigen-anything... these concepts have been so corrupted by the Brownian motion of poor translation that they're totally diffused from the original meaning; a mere hazy cloud of related concepts loosely distributed around what the original German physicist actually meant. ...so I'll need a lot more time before I can decide whether our cited source is "wrong" or just "factually misappropriated." If you would like a source in English, I highly recommend the book I mentioned above, Classical Dynamics. The proof of equivalence between the Newtonian formula and various minimization principles are shown. Marion and Thornton show the Lagrange minimization, but there's an entire chapter on calculus of variational functions; and I assert that if you can understand that chapter, you can trivially show the D'Alembert principle, and the Gauss formulation, are all equivalent.

Regarding your confusion on constraints: this sounds like a great chance to use the phrase, "an exercise left to the reader." Actually, the choice of whether an effect is a "constraint" or a "contributing factor to a generalized potential-energy field" is entirely one of preference. If you treat it as a potential energy field U, then force F = -∇U. If you treat it as an equation of constraint, then you will calculate a minimization, and you'll have a residue exactly equal to F. This can be worked analytically, but ultimately its justification comes down again to an axiomatic definition of "force." Nimur (talk) 16:58, 12 April 2012 (UTC)

Sorry, perhaps I wasn't clear: I don't believe I was or am confused about the constraints satisfied by systems that can be modelled by Hamiltonian mechanics (though perhaps I am). I'm not quite sure what you mean above about constraints: do you mean that non-holonomic constraints (i.e. velocity-dependent potentials) can be treated differently, attaining a mathematically different formulation of the system such that all constraints are holonomic and further that Hamilton's principle can be applied?

But primarily, what I am confused about is how energy conservation can be derived from Newton's laws. It is not mathematically unsound to define a Hamiltonian system with an explicit time dependence (which I think has to be in the form of one or more time-dependent potentials), and such a system does not conserve energy, though it does conserve momentum. I believed I had a counterexample to energy conservation being derivable from Newton's laws.

Two particles of equal and opposite momenta hit one another and coalesce to form a stationary, composite body. Before impact, the particles had some kinetic energy, but on coalescence, they have none.

Though I am open to the idea that this is facile. Thanks for the book recommendation, I'll try and find the book in my local library.--Leon (talk) 18:11, 12 April 2012 (UTC)

Perfect Newtonian particles do not coalesce. By introducing inelastic collision, you're no longer dealing with idealized point particles. You have implied a new force (i.e., a new reservoir of binding energy), but only defined it in a very loose way ("the particles stick together when they collide"). Nimur (talk) 19:07, 12 April 2012 (UTC)

...or the energy is dissipated as heat through distortion of the colliding objects (think of two lumps of plasticine). On deriving conservation of energy from Newton's laws, surely integrating the third law over all space (effectively $\scriptstyle \Sigma \mathbf {F} =0$) results in constant energy. SpinningSpark 19:15, 12 April 2012 (UTC)

furnace fumes

I had a 95% efficient gas furnace installed and they vented it out the side of the house on the first story. When I go in the backyard and the furnace is on you can smell these very noxious fumes coming out. They smell like chlorine and it makes you nauseous to breathe them. I'm wondering what is in these fumes and is it harmful? — Preceding unsigned comment added by 64.38.226.84 (talk) 21:31, 11 April 2012 (UTC)

1) Venting the furnace out the side of the house sounds very wrong, to me. Why can't they vent out the roof, as usual ? Please tell me they didn't use the vent from the clothes dryer.

2) The smell could be some component, like new PVC piping or a coating/film on metal ductwork, giving off fumes. If so, hopefully it will go away with time.

3) It could also be unburned gas. That doesn't smell like chlorine, usually, though. If that's what you're smelling, something is seriously wrong and there's a potential for an explosion. I'd call the gas company to ensure that this isn't the issue, then call back the furnace installers and get them to fix it. Note that high efficiency furnaces suffer from a problem (the exhaust cools down so much it causes water vapor from the burned gas to condense). If they haven't addressed this properly, it could drip down and extinguish some of the flames, causing unburned gas to be vented.

4) This sounds potentially dangerous, so I'd turn off the furnace (except for when demonstrating the problem) and use electrical space heaters until you get the furnace fixed. If you're in the Northern Hemisphere, heating requirements this time of year should be minimal, so this won't cost as much as it would in January. StuRat (talk) 21:39, 11 April 2012 (UTC)

What type of gas are you burning with it? What country are you in? 110.151.252.240 (talk) 21:45, 11 April 2012 (UTC)

This thing about venting furnaces out the side of the house is a disease in Wisconsin - haven't seen it in some other states. If you think the fumes are bad you should just hear the noise of the contraption, like a giant idiot demon with a very bad musical instrument. I hope your reaction indicates these things are indeed unheard of in the First World. It could be undesirable products of either methane or propane, I'm not sure which, but I don't think any other gasses are used. I know methane can create formaldehyde gas, which has a strong smell very vaguely akin to chlorine (it's small and oxidizing, anyway). Propane can produce carbon monoxide. For either it's not uncommon for the pieces of plastic PVC pipe to come unglued inside the house, or for there to be some hole in the wall near the vent, etc., allowing fumes to come back into the building. Basically yes, as dumb as it sounds, only more so. Wnt (talk) 21:57, 11 April 2012 (UTC)

Everyone I know seems to think that formaldehyde smells like chlorine, but I think it smells like almonds (and I think cyanide just smells god aweful and not like almonds at all). If you're getting incomplete combustion of methane, then your smell could very well be formaldehyde, but that's entirely inconsistent with the furnace being highly efficient. Formaldehyde isn't nice to breath in, but it might just be indicating a far worse problem; if you are getting incomplete combustion, then carbon monoxide is almost certainly present as well and that stuff is much more toxic but is odourless. It's unlikely you'd get any ill effects if you only breath it in when you're outside though. Leaks inside the house could be deadly if they go unnoticed. 110.151.252.240 (talk) 22:07, 11 April 2012 (UTC)

Hmmm, almonds smell like cyanide, or vice versa... maybe you're smelling more of the carbon and they're smelling more of the oxygen? Wnt (talk) 22:18, 11 April 2012 (UTC)

You don't smell individual elements in a compound. You might smell individual functional groups, though, and it is definitely true that different people can detect different chemicals through smell (it's genetic, I think). --Tango (talk) 21:00, 12 April 2012 (UTC)

True enough, though I doubt that the affinities for odorant receptors really line up very precisely with functional groups either for things this small. What I mean is that H-C-N and H₂C-O each have one carbon linked to one more electronegative atom; Cl-Cl has two electronegative atoms. In concept, an odorant receptor with a pocket sized to fit two atoms plus miscellaneous hydrogens might interact either with the slightly positive carbon end or with the electronegative end, though I make no guarantee that's how this works. Wnt (talk) 05:30, 14 April 2012 (UTC)

Venting of furnaces through the side of the building is very common these days. In fact, it's the recommended way of venting modern, high efficiency direct-vent furnaces. High efficiency furnaces capture enough of the heat that you can't get a reliable draft up a 2 story (or even a 1 story) chimney. Not venting through the side of the building is a safety hazard, as the combustion gases would back up. The flip side is that because of the efficiency, there is much less of a issue with the incomplete combustion gases that were typical with older furnaces, so it's much safer to vent near ground level. (Although there are typically placement restrictions regarding doors/windows/etc. which attempt to minimize accidental human-exhaust interaction.) - If you're getting a strong smell from a modern furnace, you should call a furnace repair person, as it likely indicates that the furnace is not performing properly, which is not only a safety hazard, but also indicates you're likely wasting money due to reduced efficiency. -- 140.142.20.101 (talk) 01:49, 12 April 2012 (UTC)

I'm wondering if the OP's description is that of Nox. It can be a bit unpleasant and acidic if you're only used to fresh air. --Aspro (talk) 22:17, 11 April 2012 (UTC)

Do you mean nitrogen oxides? Wnt (talk) 22:18, 11 April 2012 (UTC)

Specifically, mono-nitrogen oxides, abbreviated NOx, not Nox. StuRat (talk) 22:19, 11 April 2012 (UTC)

Ah, Somebody noxed not only what I meant but can remember to keep their finger on the shift key too  :-) --Aspro (talk) 22:29, 11 April 2012 (UTC)

Since we're getting technical, it's actually NO_x. 203.27.72.5 (talk) 02:32, 13 April 2012 (UTC)

The problem with trying to cure it with a catalytic converter is that it might cause 'back pressure' and the gas furnace might not operate properly – and perhaps even allow CO to enter the home. In the old-days when we wanted to keep warm, we just rubbed two boy scouts together but I guess that's not allowed anymore.--Aspro (talk) 22:38, 11 April 2012 (UTC)

Which could be solved with an exhaust fan, but now we have extra complexity and monthly expenses, so why not just use the safe, older design, and give up on so-called "high efficiency" furnaces ? StuRat (talk) 22:51, 11 April 2012 (UTC)

it uses natural gas, and i have had it for 6 months — Preceding unsigned comment added by 64.38.226.84 (talk) 00:21, 12 April 2012 (UTC)

And it just started to stink ? Sounds like something changed then. Perhaps some PVC part that's supposed to be up in the cool part broke off and fell down to the hot part. StuRat (talk) 01:56, 12 April 2012 (UTC)

Answers to similar question on three forums:

• Shouldn't smell like auto exhaust but if it's natural gas it should smell like acid or chlorine
• But I always wonder why "clean combustion" tends (to me at least) to have a smell that is somewhat like "chlorine", in the swimming pool smell variety. Must be something else, but the smell is quite common from "high efficiency" furnaces, and from some cars as well.
• They do smell nasty! My Dad in the UK said the same thing about his 90%+ unit.

High efficiency is lower exhaust temperature, slower rising, more smell?... Ssscienccce (talk) 16:15, 12 April 2012 (UTC)

And don't forget the side discharge. Hot exhaust on the roof will rise, while cool exhaust at the side of the house will hang about. StuRat (talk) 17:33, 12 April 2012 (UTC)

I read somewhere that the fumes contained aldehydes is that true? The furnace produces a water which is drained into a utility sink via a pump. The installer told me that the water is acidic about pH 2. I also wonder if the fumes the furnace produces are also acidic. --64.38.226.87 (talk) 19:57, 12 April 2012 (UTC)

Note that if we start getting into whether it's safe for you to breathe the fumes from your furnace, that's actually a sort of "medical advice" we're not qualified to give. Besides, opinions can vary pretty drastically about the effects of small amounts of environmental toxins - for example, I have seen papers claiming that formaldehyde can somehow reduce intelligence of laboratory workers, while other people don't worry about it much. Bottom line is, we have no real idea how much it stinks or what the chemical is, so we surely can't tell whether it's safe. Wnt (talk) 20:34, 12 April 2012 (UTC)

I think a pH of 2 will dissolve your pipes in short order. This furnace sounds like a worse idea every minute. (Maybe you could save the plumbing by draining into a bucket containing baking soda, to neutralize it, before it overflows the bucket and goes down the pipes ?) StuRat (talk) 05:38, 13 April 2012 (UTC)

science

how can i measure water liquid level using a co-axial capacitor? how is the change measured and fed to a digital device such as an AVR kit to display the output in a LCD board.which circuit is the most suitable for determining the level of the water? — Preceding unsigned comment added by Irishgut3 (talk • contribs) 23:07, 11 April 2012 (UTC)

Sounds a bit like a homework question. But we do have an article.Level_sensor#Capacitance--Aspro (talk) 23:24, 11 April 2012 (UTC)