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May 10

Constellations of stars

where to look for it : the Big Dipper, the Little Dipper, the Orion and the Andromeda? —The preceding unsigned comment was added by 72.187.17.165 (talk) 00:08, 10 May 2007 (UTC).[reply]

I'm not sure what it is that you're looking for: we have articles on the Big Dipper, the Little Dipper, Orion, and Andromeda. We also have an article on star chart that will link you to a useful star map. Let us know if you were looking for something else. - Nunh-huh 00:19, 10 May 2007 (UTC)[reply]

Stellarium is my favourite way to locate things in the sky. It's the easiest star software for beginners because it very closely mimics what you actually see with your eyes. Vespine 00:21, 10 May 2007 (UTC)[reply]

Where to look for these in the sky depends totally on where you are on earth, and the time of year. Orion, in particular, is not visible all year from most places, though it is unmistakable. Get yourself a cheap pocket planisphere from anywhere that sells telescopes.--Shantavira 08:50, 10 May 2007 (UTC)[reply]

Measuring Potential Difference

[[Image:NonFreeImageRemoved.svg -->|thumb|When in doubt, use electrochemistry!]] Hello. If electrons are not flowing into the circuit, is it possible to measure the potential difference across the terminals of the dry cell? Thanks. --Mayfare 00:31, 10 May 2007 (UTC)[reply]

In theory: no. In practice: no. Please see voltmeter. To measure a voltage, one needs a current. With an exceptionally good insturment, the current can be exceptionally small, but some electrons must flow. -Arch dude 01:41, 10 May 2007 (UTC)[reply]

An electrostatic voltmeter draws no current (not even a little bit). Also see potentiometer for measuring voltage: no current is drawn at balance. —The preceding unsigned comment was added by 88.110.183.42 (talk) 02:03, 10 May 2007 (UTC).[reply]

Well, no continuous current. There's still a transient, and probably a very small leakage current. -- mattb 05:20, 10 May 2007 (UTC)[reply]

The link is at electrometer. And in principle, a virating-reed electrometer could draw no current, not even a charging current (if the vibrating reed were placed near but not in contact with the already-charged object). Electrons would flow on the charged object but none would "leave".

Atlant 12:30, 10 May 2007 (UTC)[reply]

So many electrical engineers and so few chemists! You could calculate the electric potential based on the concentrations of the chemical in the battery. See dry cell for the OP's question, and electrochemical cell for a brief discussion of how to do this. Nimur 08:19, 10 May 2007 (UTC)[reply]

There are quantitative details at Standard electrode potential, with examples, and this [[:Image:NonFreeImageRemoved.svg -->|handy chart]]. Nimur 08:21, 10 May 2007 (UTC)[reply]

A potentiometer in the older sense was a bridge device with a standard cell, a slidewire and a galvanometer. The standard cell furnisshed a relativly constant voltage with a correction for temperature. Certainly tiny currents flowed from the standard cell and the external source of EMF to be measured as the slidewire was adjusted to null the current, but it was likely microamperes or less. At the instant when the voltage was said to be "measured," i.e. determined, no measurable current would be flowing, as shown by the non-deflection of the galvanometer. A modern digital voltmeter such as the Fluke 87V has a 10 megohm input impedance, so is if is measuring say a 1.5 volt emf, it would draw 0.15 microamperes. If it were measuring the max allowable voltage of 1000 volts, it would draw 100 microamperes. In a potentiometer bridge circuit, this could be reduced to a fraction of a microampere.Vacuum tube voltmeters from the 1940's on had this high or higher input impedances. Edison 16:05, 10 May 2007 (UTC)[reply]

Shouldn't it be 'yes', it is possible to measure the potential difference, but it will be 0 :] HS7 17:54, 10 May 2007 (UTC)[reply]

HS7: No, it is not zero. The potential difference is unquestionably there when there is no current flowing; the question was whether it can be measured without drawing current. --169.230.94.28 00:58, 11 May 2007 (UTC)[reply]

Principle,law,hypothesis,theory.theorm

What is the difference between principle, theory, theorm, law and hypothesis? —The preceding unsigned comment was added by Invisiblebug590 (talk • contribs) 08:04, 10 May 2007 (UTC).[reply]

Principle, theory, theorem, physical law, and hypothesis? Laws of science seems to be a good introduction as well. Nimur 08:25, 10 May 2007 (UTC)[reply]

Embalming and eyes question?

This is a bit morbid but I just want to know whether the eyeballs are removed for embalming and are the eyelids sewn or closed shut in some way like the mouth? I remember hearing somewhere that the eyelids are sewn shut to stop them 'popping' open during the viewing and that many years ago a penny would be placed on each eyelid for this reason. I don't know whether this was ever really done or whether it was instead a cultural/tradition thing but have always wondered about it and thought more about it recently when thinking about organ donation and the eyes were on the list. I'd appreciate any relevant answers or info, particularly from morticians/embalmers. Jocee 13:18, 10 May 2007 (UTC)[reply]

There are two methods that are widely used for keeping the eyes shut. The most common is the "eye cap", which is a bit like a contact lens with "grippers". It's placed under the eyelids, over the eyeballs, and keeps the lids in position. Another less-used technique is to glue the lids together. Eyeballs are not removed. Even if the corneas have been donated, it's just the corneas that are removed, not the entire eyeball. Coins on the eyes is a very old tradition, but usually explained religiously (e.g. payment for Charon's ferry) rather than practically. - Nunh-huh 13:36, 10 May 2007 (UTC)[reply]

I always assumed that the coins were placed on the eyes to assure that as rigor mortis set in, the eyelids were closed; if they were open at that time, it'd be impossible to fix until after the rigor had passed. ("He's not dead, he's just starin' at Wikipedia! Honest -- hold a mirror to his mouth!")

Atlant 16:34, 10 May 2007 (UTC)[reply]

The timing of rigor mortis makes it unlikely that this would be the reason unless the coins are placed there as soon as death occurs and would only be useful if the body is being displayed fairly shortly thereafter. Many people forget that rigor mortis is only a transient state. DMacks 16:54, 10 May 2007 (UTC)[reply]

According to our article, you've got 3-4 hours to get the coins on, else Aunt Bertha will be staring at you for the next 36 hours. And lots of people don't die by surprise, so application time often wasn't a factor.

Atlant 22:25, 10 May 2007 (UTC)[reply]

Freezing Points

Hello, My question is: What is the freezing point of a 25mM sodium bicarbonate solution? —The preceding unsigned comment was added by 208.38.54.242 (talk) 15:28, 10 May 2007 (UTC).[reply]

See our article about freezing point depression to learn how to calculate this. DMacks 16:15, 10 May 2007 (UTC)[reply]

Why elliptical orbits?

This is not an assignment, it is simply a discussion. My teacher suggested that I post it here. We were wondering why planets travel in an elliptical orbit? Why not just a circle? What is the other focal point? We haven't found it anywhere, but we're looking. Thanks for any insight you can give us! Someone999456 17:43, 10 May 2007 (UTC)[reply]

Hmm, tough one. I can't answer your question outright, but I suggest you take a look at Kepler's laws of planetary motion Ai y da 18:26, 10 May 2007 (UTC)[reply]

Our orbit article says that there is "nothing present at the other focus." --LarryMac | Talk 18:27, 10 May 2007 (UTC)[reply]

Orbits can be perfectly (or very nearly) circular, but it takes some very precise starting conditions - given the immense number of "non-circular" orbits compared with the (technically one) truly circular orbit, its no surprise that most orbits seen are elliptical, as a matter of probability. As for what is present at the other focus of the ellipse - as far as I'm aware, this has no real physical meaning, and is just an artifact of the mathematical description - someone please, correct me if I'm wrong. Of course you could say it's the point at which the orbit would be unchanged if the orbitted body was moved to it... Icthyos 18:30, 10 May 2007 (UTC)[reply]

The fish's last sentence is wrong because the speeds would be wrong. —Tamfang 02:00, 11 May 2007 (UTC)[reply]

(eC) Kepler's laws of planetary motion are just applications of the usual laws of nature involving moving objects (force, inertia, gravity, etc). In addition to that Kepler page, see also Orbit equation and Orbital mechanics for various levels of related mathematical and physics discussions. The simple answer for "why not a circle" is because as the Earth (for example) swings past the Sun (for example), it's moving too fast for gravity to slow it down and pull it back around in a circle (note that there are cases of circular orbits, but they are relatively rare; you can think of a circle as just a special case of an ellipse, one where the two focci are at the same point). There's nothing really "at" the other focal point per se. DMacks 18:31, 10 May 2007 (UTC)[reply]

A circle is a type of ellipse (where the minor axis equals the major axis and the two focus points coincide). Consider what would happen if all orbits started as circular. After that, any impact or gravitational tug from nearby planets or objects would perturb it into a non-circular elliptical orbit. StuRat 20:25, 10 May 2007 (UTC)[reply]

Another way to look at it is that an ellipse forms a perfectly stable orbit - with all of the forces on the planet in perfect balance the whole way around. There is simply no left-over force to pull the orbit into a circle...so from an energy perspective - it makes no difference whether your orbit is elliptical or perfectly circular. SteveBaker 21:06, 10 May 2007 (UTC)[reply]

This question seems somewhat similar to the oft-asked question "Why do the vast majority of planets spin on an axis?". There's absolutely no reason for them to not spin, or orbit elliptically, considering the effectively random conditions that they formed under. Circular orbits and no rotation are such incredibly precise conditions for a planet to have that it's almost impossible. 213.48.15.234 09:00, 11 May 2007 (UTC)[reply]

SteveBaker's suggestion that the forces are balanced in an elliptical orbit cannot be true - negating perturbations from other planets, there is only one force acting on the planet - from the Sun. It's all basically down to how much angular momentum the planet has. Angular momentum is constant throughout time for a planet - neglecting perturbations from other objects.

In an ellipse, near to perihelion, the planet has more angular momentum than a planet orbiting in a circle at that distance (so will begin to draw away from the sun). Near to aphelion, the planet has less angular momentum than a planet orbiting in a circle at that distance (so will begin to fall inwards towards the sun). Angular momentum increases with distance from the sun for planets in a circular orbit, i.e. Earth has much more angular momentum than Venus, despite similar mass and Venus travelling faster.

So it will not orbit in a perfect circle, unless it had the required angular momentum to match that for a circular orbit at that distance from the sun. As angular momentum for a circular orbit rises as distance from the Sun increases, an object which is getting further from the Sun soon falls behind on the required angular momentum (because its individual angular momentum is constant through time), so it falls back inwards into the solar system, where it suddenly gets ahead of its angular momentum requirement, so it rises back outwards from the Sun. It might have enough speed in the first place to escape completely, but that is another question.Richard B 13:49, 11 May 2007 (UTC)[reply]

I thought the other focus of the planets' orbits was the center of mass of the solar system? --⁪froth^t 18:49, 15 May 2007 (UTC)[reply]

Since the orbits have different eccentricities, and their long axes point in all different directions, they can hardly have a common second focus. —Tamfang 23:12, 15 May 2007 (UTC)[reply]

life question

If the sun were to switch off instead of exploding and destroying the earth, would the bacteria that live in volcanoes and use sulpur as a source of energy, or the creatures that eat them, ever evolved into an inteligent, human-like specis? And would they be able to live outside of the volcanoes, somehow extracting sulphur from rocks? Apart from these, are there any other possible sources of energy that living organisms can use if there wasn't a star nearby? HS7 17:50, 10 May 2007 (UTC).[reply]

First of all, assuming that the outward pressure supplied by the sun's nuclear fusion is replaced in equal quantity (ie preventing the sun from collapsing on itself), then on a simplistic level, we wouldn't actually notice any difference - since the mean free path of the photon within the sun is so small (typically a few mm according to [[Sun#Core|the article]) the photons' "travel time" between being produced and reaching Earth is around a million years or so, though the lower limit given in the article is 17,000 years - we certainly wouldn't notice a lack of sunlight without our generation - Just an aside.

As for life continuing on without the light of the sun - I'm skeptical. Perhaps some xenobiologists could help out? Icthyos 18:25, 10 May 2007 (UTC)[reply]

I see no reason why life in, say, deep oceans wouldn't continue to exist for quite some time, as the sun has little to no energy input in those systems. Ecosystems surrounding black smokers would be one such example. However, evolving from that state to one of human-level intelligence is quite a stretch. — Lomn 20:03, 10 May 2007 (UTC)[reply]

Yeah - it's not that life up here on the surface is somehow preventing those creatures from evolving - it's that in their ecological niche - they are better off being how they are right now. Whilst there is energy to be had in those weird setups - it's pretty pathetic compared to sunlight - my guess is that they are using all the energy they can get just to be what they are now. It's a commonly held myth that all creatures evolve towards the pinnacle of intelligence and everything is moving steadily "up the evolutionary ladder". Evolution doesn't work that way - it works to provide the best match between the creature and it's environment. That can also mean evolving to be less sophisticated - smaller, weaker, slower or more stupid. When ordinary land creatures get stuck in a deep dark cave (where their eyes are useless) - they gradually evolve so as not to have eyes anymore. Whilst that seems like a setback for them - it's quite the opposite. By not spending the energy required to make and maintain eyes - and all of the brain to make use of them - the creature has more energy left over for reproduction - and that's all evolution "cares about". SteveBaker 21:03, 10 May 2007 (UTC)[reply]

Steve, are you sure that life up here couldn't, at least in principle, be impeding the evolution of those creatures? Sidestepping the practical question of survival of life without sunlight... if most life on earth were magically destroyed, wouldn't we expect to see adaptive radiation among the survivors? --Allen 03:12, 11 May 2007 (UTC)[reply]

I don't see how - they use completely different resources to creatures at the top of the water column and on land - it's hard to imagine what we could be doing to prevent them from evolving - they are trapped by their very weird life-styles. But you are certainly correct in saying that if we all magically disappeared one day, they would evolve to fill our niche - but that wasn't the question. The questioner specifies that all of the resources in the 'upper world' have vanished due to the abrupt loss of sunlight - so there is no resource for these creatures to evolve to take advantage of. Heat from the earth's core is the only remaining source of energy for them to extract. SteveBaker 03:30, 11 May 2007 (UTC)[reply]

You're right; I think I misunderstood the emphasis of what you had said. --Allen 03:49, 11 May 2007 (UTC)[reply]

There is evidence that there are no organisms or groups of organisms living on earth which are independent of the sun's energy for life, including the above-mentioned deep-sea vent communities. This was discussed (though consensus was not reached) on this reference desk in an article entitled "when the sun goes red giant" which was at least partially edited on September 27, 2006, I don't know how to link this conversation personally, but perhaps someone else could help me out. ^tucker/_rekcut 22:40, 10 May 2007 (UTC)[reply]

[I provided your link.] --Tardis 23:09, 10 May 2007 (UTC)[reply]

Shouldn't all life on the top of the planet cease to exist in such a contest? Wouldn't it be just a giant ice cube? Bastard Soap 13:26, 11 May 2007 (UTC)[reply]

the earth did become a giant ice cube (well actually a ball but...) a while ago and a lot of life survived. But they did still have sunlight getting through the transparent ice to the water at the bottom of the oceans. So nothing could live just on the heat from the earth? How does the sun affect the sulphur creatures?

old books

can anyone reccomend any places (in england) where I can find old books. I am looking for both books that were written a few decades ago and aren't available in bookshops any more, and for books written a few centuries ago. In particular I am interested in classical greek and roman books (translated into english).HS7 18:02, 10 May 2007 (UTC)[reply]

Try Book collecting. Some folks on the Talk page there may have an interest in the subject and can speak more for where to look for these things. You're probably going to be looking at eBay or finding small book collecting shops to do this. -- Kesh 18:44, 10 May 2007 (UTC)[reply]

As places, Hay-on-Wye or the Charing Cross Road in London are certainly the ones to go for. Johnbod 20:00, 10 May 2007 (UTC)[reply]

I suppose we need to know your location a bit more precisely if we are to recommend particular brick and mortar stores. For online bookstores, I believe Amazon.com also sells used, recent books. StuRat 20:06, 10 May 2007 (UTC)[reply]

I found Totnes almost as interesting as Hay-on-Wye. —Tamfang 01:58, 11 May 2007 (UTC)[reply]

Pollination

What types of bees did most of the pollinating in the Western Hemisphere before the importation of the European honeybee? Corvus cornix 18:06, 10 May 2007 (UTC)[reply]

In my little garden I see lots of different insects visiting the flowers. If you look close, there are manny different types of flies among them. 84.160.220.235 19:37, 10 May 2007 (UTC)[reply]

That's right, it's not just bees that pollinate flowers, and not just insects, either. Hummingbirds do their share, as well. StuRat 19:58, 10 May 2007 (UTC)[reply]

paper cut

After getting a papercut, how long should I expect it to take before I can't see it any more. I've had a cut on my finger for hours and there is still a faint orange line. And is paper cut one word or two? HS7 18:06, 10 May 2007 (UTC)[reply]

You shouldn't be worried!! If all there is after a couple of hours is a faint orange line, there is no problem what so ever. I would expect it to take 1-4 days to heal, but other factors can affect it. Someone999456 21:47, 10 May 2007 (UTC)[reply]

There are many factors in healing, including your age, the location and severity of the cut, whether it gets infected, whether it's wet or dry (cuts kept moist heal much faster), and so on. I once was reading in bed and when I turned the page, got a nasty paper cut on my eyeball. I thought I'd be suffering for a while, but by the next day it had totally healed, probably due to being kept moist. You may have noticed that small injuries in your mouth heal very quickly, too. Paper cuts on fingers usually take me 2-4 days to repair. Wound healing might have more information for you. --TotoBaggins 19:01, 10 May 2007 (UTC)[reply]

Seriously, on your eyeball? Ouch! Ai y da 19:43, 10 May 2007 (UTC)[reply]

One of my friends, the same thing happened to him, but he said not to worry about it because the eye is the fastest healing of all body tissues. Is that right? [Mac Δαvιs] ❖ 01:04, 11 May 2007 (UTC)[reply]

I once cut my finger about 3mm deep with a simple sheet of paper. It took weeks to heal. I suppose, with enough bad luck, a paper can cut all the flesh right to the bone. 84.160.220.235 19:05, 10 May 2007 (UTC)[reply]

One important factor is that the two sides of the cut should be held together. Normally this isn't an issue, but if the cut is on your hands and you are using them, the cut can be stretched apart from time to time, slowing the healing process. A bandage can help with this, but also can keep oxygen out, and oxygen promotes wound healing. StuRat 19:45, 10 May 2007 (UTC)[reply]

The cut I had was clean and smooth and nearly painless. A surgeon would have been proud of it. 84.160.220.235 20:53, 10 May 2007 (UTC)[reply]

Wound glue can be helpful with these "surgical-grade" paper cuts. ;-)

Atlant 12:17, 11 May 2007 (UTC)[reply]

I once cut my foot open on the disc draw of my DVD player. It hurt like all hell and was quite deep and long. Moral of the story? Don't operate your DVD player with your toes... Nebuchandezzar 08:10, 11 May 2007 (UTC)[reply]

Doesn't a scab forming on cuts stop them separating :? I asked this question becuase I am used to my cuts dissappearing in a few hours or sometimes a day :) Is it possible to get 'out of practice' at something like that :( And I still don't know if it is one word or two :( HS7 20:01, 13 May 2007 (UTC)[reply]

Yes, but that takes some time, especially if the wound isn't held together while the scab forms. I have seen them start at the edges of a wound and then bring the two sides together, though, much like sutures. I bet this would look cool on time lapse photography, like zipping the wound closed from both ends. If the sides are two far apart, however, you end up with a scar. StuRat 22:03, 13 May 2007 (UTC)[reply]

What's the difference between a pathogen and an antigen?

What's the difference between a pathogen and an antigen? Anchoress 19:01, 10 May 2007 (UTC)[reply]

A pathogen is a whole infecting organism alive that causes pathology and disease, whereas an antigen is merely a molecule that triggers an immune recognition and reaction. An antigen is never the whole infecting organism (virus or bacteria) but a molecule on the organism's surface that is recognised (a protein or glucoprotein). Hence one infecting bacteria may be recognised by several antigens on its surface, and a purified antigen may be given on its own as a non-infectious non-pathogenic vaccination to teach the immune system to recognise and deal with the real pathogen if ever encountered. David Ruben ^Talk 19:10, 10 May 2007 (UTC)[reply]

Cool, thank you very much for that answer. Anchoress 19:57, 10 May 2007 (UTC)[reply]

I wonder if a prion could be called both an antigen and a pathogen. --JWSchmidt 19:20, 10 May 2007 (UTC)[reply]

A protein based antigen is typically only a small piece of protein, and not the whole protein, so probably not. Someguy1221 21:53, 10 May 2007 (UTC)[reply]

Also, is there any evidence that prions provoke an immune response? Anchoress 15:00, 11 May 2007 (UTC)[reply]

According to Clearance and prevention of prion infection in cell culture by anti-PrP antibodies, antibodies to prion protein can be made by mice. see also. --JWSchmidt 19:54, 11 May 2007 (UTC)[reply]

Leaf (species) identification for Commons images

I just uploaded two images to Commons, photos I took a while back at the Montreal Botanical Gardens. They're of some leaves of a particular plant which was either a small tree or a large bush. I'd like to name the species of the plant on the description page, but I have no idea what it is. If someone would identify it for me, I would be grateful, although this is low priority. Above are the two images in question (don't worry, they're GDFL/CC:SA-AT licensed). I would appreciate a reply through my user talk page if possible (use the t in my signature). Nihiltres^(t.c.s) 20:28, 10 May 2007 (UTC)[reply]

A Pawpaw trees perhaps? I would guess that it would be some member of the Annonaceae family. S.dedalus 01:29, 11 May 2007 (UTC)[reply]

Onion milk?

I just peeled away the first layer of two onions and both leaked some kind of white, watery liquid from the ends. Any idea what this might be? --84.137.28.204 20:43, 10 May 2007 (UTC)[reply]

The natural juices of the onion. Mmmm... Onion juice. Tasty! Dismas|^(talk) 20:47, 10 May 2007 (UTC)[reply]

Are you sure? I've never seen onions do this and I am kinda scared it might be poisonous. --84.137.28.204 20:53, 10 May 2007 (UTC)[reply]

Some varieties, or some ripenesses, do it; some don't. But yes, Dismas is right, it's perfectly normal, and not at all hazardous (other than to your eyes, of course! :-) ). --Steve Summit (talk) 21:11, 10 May 2007 (UTC)[reply]

Onions spoil fairly quickly, and when they do the liquid coming out is milky rather than clear. Granted, there may be onions for which the fluid is cloudier than others. Edison 23:53, 10 May 2007 (UTC)[reply]

I've cooked with such onions with no problem. Its actually rather common with the yellow onions I've bought, even the ones freshly bought from the store. I didn't even know that they were supposedly "spoiled". (Though I tend to cook them even if I see green stalks growing out.... if the bulb is brown though, it'd obviously be time to throw them out or maybe even replant.) Root⁴(one) 03:59, 11 May 2007 (UTC)[reply]

The liquid I've seen in the center of onions is clear. StuRat 03:36, 11 May 2007 (UTC)[reply]

Titration Question !

Is a titration in the lab a good way to determine the concentration of an acid or base? Thanks for any help! —The preceding unsigned comment was added by 76.188.176.32 (talk) 21:59, 10 May 2007 (UTC).[reply]

Yes. That one was easy :-) Someguy1221 22:00, 10 May 2007 (UTC)[reply]

Mhmm.. any reasons why???

Well, the point of an acid-bade titration is to determine what relative quantities of an acid and a base (one of known concentration, one of unknown concentration) achieve a certain pH (indicated by a change in color of the indicator chemical you're using, usually phenolphthalein). Practically, it's the easiest and most error free way to directly measure the concentration of an acid/base without using an actual pH meter (that I know of). Someguy1221 22:10, 10 May 2007 (UTC)[reply]

Technically, titration could even be seen as more accurate than using a pH/ion electrode since electrochemical measuring devices actually quantify the ionic activity—which can be affected by temperature, concentration, etc. -- MarcoTolo 23:17, 10 May 2007 (UTC)[reply]

The titration is an excellent way of determining the concentration of an acid or a base, however you do need to know a few things first! Whether you're dealing with a weak acid or base, as this will effectthe indicator that you need to use, as the end point will have a different pH. You also need to know wether the acid or base you are assaying is monobasic/acidic or mutibasic/acidic, as this will affect the stoichometry of the chemical equation, and therefore the amount of acid or base present. To work out the amount of acid or base present you need to know the chemical formula or the relative molecular mass of the acid/base. Using the formula Mass = Relative molecular mass/moles, and Moles = Volume x concentration (in moles/dm^3)/1000 you can work ou the number of moles of acid/base you used to titrate, and then adjust for the stoichometry, and you have the moles of base/acid used.

Climate /United States/lowest rainfall

What is the place and amount of the lowest average rainfall? —The preceding unsigned comment was added by 71.143.16.157 (talk) 23:02, 10 May 2007 (UTC).[reply]

The nation’s driest area is the Desert Southwest, specifically southwestern Arizona, southern Nevada and southeastern California. The average annual rainfall across most of the region is less than 5 inches per year. This area includes the driest large city in the USA – Yuma, Ariz., which receives just less than 3 inches annually. —Preceding unsigned comment added by 76.188.176.32 (talk • contribs) 23:31, 10 May 2007

And Death Valley gets less than 2 inches of rain per year. StuRat 03:34, 11 May 2007 (UTC)[reply]

Titration

This is a continuation of a previous asked question ..

Are there any limitations to the titration method? What are they? —The preceding unsigned comment was added by 76.188.176.32 (talk) 23:25, 10 May 2007 (UTC).[reply]

Yes. The titration method cannot readily be used to make a planet-eating robot, to name but one. Can you be a little more specific about what kinds of limitations you're looking for? Algebraist 11:17, 11 May 2007 (UTC)[reply]

Going back to my high school and college chem classes many years ago, an obvious limitation is that the user must make a subjective determination of whe he has dripped enough of a reagant into the solution to cause a color change, which has an inherent subjectivity. The process is repeated with the two sources and the amounts noted, to use statistical averaging to achieve a more precise number. Edison 13:18, 11 May 2007 (UTC)[reply]

The first thing I thought is that titrations are only good at quantifying concentrations of acid or base (not, for example, concentration of glucose or sodium chloride). This is because there are no good glucose-neutralizing additives, nor are there easy brightly-colored indicators. The premise of the titration is that adding Substance B will neutralize Substance A; this might be extended to some non-acid/base reactions, but it could never be generalized to quantify any type of solution concentration. Nimur 07:03, 12 May 2007 (UTC)[reply]

Historically, titrations didn't just involve acid-base reactions, but also other reactions such as redox and precipitations. There are methods in the literature for titrating both glucose and sodium chloride, not that they would be used nowadays. I think the main limitations of titration are accuracy and speed. Hexane2000 08:24, 12 May 2007 (UTC)[reply]

I'd be interested to see that literature! Nimur 07:48, 13 May 2007 (UTC)[reply]