Wikipedia:Reference desk/Archives/Science/2009 January 18

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January 18

Can I buy cyanide being 16 year old

It's to separate a rock from gold. Hope you understand me, I am not English-Native. --190.49.126.240 (talk) 03:16, 18 January 2009 (UTC)

In what jurisdiction? Algebraist 03:23, 18 January 2009 (UTC)

You could extract it from apple seeds. Our article on cyanide gives a cursory overview of the process. Still, there are likely easier methods of extracting gold from ore than attempting a home Au/CN complex reaction... --Jayron32.talk.contribs 03:40, 18 January 2009 (UTC)

Sigma-Aldrich sells cyanide, though you would probably need a credit card to buy it and you would have to check with local laws. Here is the link to Sigma Argentina. Rockpocket 03:44, 18 January 2009 (UTC)

I AM IN ARGENTINA. --190.49.126.240 (talk) 03:47, 18 January 2009 (UTC) JAYRON, and what can I do if it's not with cyanide, does the article of Wikipedia explain it? --190.49.126.240 (talk) 03:48, 18 January 2009 (UTC)

Thank you Rockpocket. Thank you everyone. And if I can't buy cyanide, does a hammer work? —Preceding unsigned comment added by 190.49.126.240 (talk) 03:50, 18 January 2009 (UTC)

Yes, the hammer sure works. We have lots of information on various methods of gold mining and gold extraction. By the way, the latter article suggests that thiosulfate may be used to extract gold. If sodium thiosulfate indeed works, then you can just go to a photography supplies store and buy as much of it as you want. They probably sell it as hyposulphite of soda, or simply hyposulphite. And, most important, just enjoy the scenery as you travel; you may or may not get rich, but Argentina is the most beautiful country I've ever been to, and I've been to many. --Dr Dima (talk) 06:13, 18 January 2009 (UTC)

It goes without saying that cyanide is not the most environmentally friendly thing to mess with! Gold is relatively easy to extract because it doesn't chemically react with the rock - so you only have to physically separate it - not do any messing around with chemicals. If you can merely crush the rock small enough (and on a small scale, a hammer should be fine for doing that) then you can use the 'panning' technique to separate out the heavier stuff - which will be mostly fairly pure gold. Our article Placer mining has some fairly concise instructions on that - and other physical separation techniques. SteveBaker (talk) 07:05, 18 January 2009 (UTC)

Agreed. Cyanide poisons the water and kill animals (and maybe people). If it isn't illegal, it should be. StuRat (talk) 11:03, 18 January 2009 (UTC)

Even without cyanide, large scale gold extraction is a disaster for the ecology of the area because of the large amounts of water required - and the 'tailings' (left-over crushed rock) getting washed downstream and eventually silting up something that wasn't silted up before. But an individual with a hammer and a gold pan hunting for nuggets in a stream won't do significant damage. SteveBaker (talk) 16:59, 18 January 2009 (UTC)

Can I buy cyanide, being much older than 16? Seriously, can any adult just buy cyanide from a chemical supplier without special licensing and whatnot? As a well known poison, I would have thought that it's distribution would be regulated, even for adults. Dragons flight (talk) 01:29, 19 January 2009 (UTC)

Yes, but considering how many other poisons are readily available, like antifreeze and wood alcohol, it would be difficult to ban all poisons. StuRat (talk) 01:34, 19 January 2009 (UTC)

I don't think that is a fair comparison. Many people use and need antifreeze. How many people outside specialized industries need cyanide? Not to mention that it is relatively easy to make the poisonous gas hydrogen cyanide from most cyanide salts. How many poisons do you use that readily form poisonous gases? Dragons flight (talk) 01:45, 19 January 2009 (UTC)

Bleach? APL (talk) 02:34, 19 January 2009 (UTC)

Yes, I believe chlorine bleach and ammonia mix to produce deadly chlorine gas. StuRat (talk) 15:21, 19 January 2009 (UTC)

Both of the items I mentioned have relatively safe alternatives. There's non-toxic automotive anti-freeze, and ethanol can be used for cleansing wounds just as methanol can. Ironically, it's not legal to sell ethanol for such purposes, as the government is afraid people will drink it and the gov will lose their alcohol tax income. So, we get a poisonous alcohol to use instead. (But, of course, the amount absorbed through the skin isn't enough to be toxic.) StuRat (talk) 15:13, 19 January 2009 (UTC)

I don't think I've every seen methanol used to clean a wound, though isopropyl alcohol is used pretty commonly in my experience. Where do you find methanol being used to clean wounds? --Scray (talk) 17:31, 19 January 2009 (UTC)

In my experience, it's not easy to buy isopropyl alcohol in the UK. I got asked questions about what I needed it for when I last tried to purchase some - and I had to try four different places before I found one that would accept "to soak my print head in overnight" as a legitimate reason. I'm still not entirely sure why. --Kurt Shaped Box (talk) 17:41, 19 January 2009 (UTC)

They didn't accept your first try when you said "to poison my mother-in-law's drinks" ?  :-) It's completely unregulated in the US. StuRat (talk) 20:30, 19 January 2009 (UTC)

Depends on the country. Cyanide in Australia is governed by the Poisons Act 1964. A licence or permit is required for the purchase, sale and use of cyanide from the Department of Health. But in the US, it seems its perfectly legal to by cyanide, as long as you have a legal reason for doing so. See this article about a man who bought a pound of cyanide, telling the company that sold it to him that "he needed it to clean jewelery". Rockpocket 03:05, 19 January 2009 (UTC)

Cyanide shouldn't be handled by just anyone. A person should be fully trained and understand the very significant dangers there are when handling it. I would advise a 16 year old to avoid it regardless of the legalities. It's just not something to be casual about. 89.159.158.241 (talk) 03:51, 19 January 2009 (UTC)

Chest pain

I'm looking for medical conditions that can be mistaken for a heart attack other than heartburn. (Everybody knows that when a fictional character has sudden, severe chest pain, it's either a heart attack or acid reflux. I want something different.) --Carnildo (talk) 06:08, 18 January 2009 (UTC)

What's the fictional purpose? If you want it to be a "false alarm" you could choose costochondritis. If you want it to have consequences, it could be an old fishbone that was accidentally swallowed two weeks ago and has now caused esophageal rupture. Anyway, you'll find ideas by googling "chest pain differential diagnosis", and you can pick what you like. Echinococcus granulosus anyone? - Nunh-huh 06:17, 18 January 2009 (UTC)

Pleurodynia seems like it might fit the bill. --Scray (talk) 06:44, 18 January 2009 (UTC)

Our article on Chest pain lists a couple dozen causes. 152.16.16.75 (talk) 11:35, 18 January 2009 (UTC)

A heart attack can appear as a sore shoulder or a sore jaw. Lifting something heavy could cause a sore shoulder. Chewing something tough could cause a sore jaw muscle. Hope this helps. Edison (talk) 22:41, 18 January 2009 (UTC)

related to physics

Hi, I would feel extremely happy if I could get details about the structure and characteristics (like no.of atoms per unit cell.co-ordination number,atomic radius, packing factor, density) for the following crystals:NaCl, ZnS, graphite, diamond along with the diagrams. Thanks

Have you looked in our articles sodium chloride, zinc sulphide, carbon, graphite and diamond? SpinningSpark 15:36, 18 January 2009 (UTC)

knowledge key

Iam asmart person,i got that wish to have deep understanding for evry thing , i tried so mush , and with the time i found out that its impossible ,because evry question will lead you to anther question , at the end iam willing to focus on my title , iam acivil engineer , i'd like to understand the basics of structural analysis step by step , some thing so detailed ... thank you ...??? —Preceding unsigned comment added by 94.249.18.171 (talk) 14:37, 18 January 2009 (UTC)

You could start off with our structural analysis article and then read all the articles in the navigation box. There is also a Wikibook on strength of materials. You might also be interested in Business English as you will need to write reports now and then in Civil Engineering. SpinningSpark 15:22, 18 January 2009 (UTC)

dim flashes from a Fluorescent lamp

My room has a circular Fluorescent lamp installed. When I turn it off, the room is totally dark save from a few electronic lights from various devices. I know that these type of lamps emit phosphorescence for a while after it is switched off. However, I sometimes see some part of the circular lamp momentarily flash more brightly than the others. One time, it flashed and dimly lighted my room before turning off again. My question is, what would that flash be? --Lenticel ^(talk) 15:18, 18 January 2009 (UTC)

This is only a guess but. . .discharge from the ballast choke? SpinningSpark 15:51, 18 January 2009 (UTC)

I have seen fluorescent lights continue to flash dimly when the wiring is incorrect, such that the neutral is being switched rather than the hot wire, or when there is a "sneak circuit" backfeeding the lamp from some other source. I would check for this if the lamp continued glowing dimly or flashing occasionally long after it was turned off. If it is just one flash right after turnoff it could be as stated above. Edison (talk) 19:53, 19 January 2009 (UTC)

I think the sneak circuit scenario might be plausible since it does glow for a little while from time to time. The lamp dangles from a wire tethered to the roof rather than fixed in a ceiling, (my room sorts of "leans" on the main house, its roof only has a layer of insulation rather than a ceiling).--Lenticel ^(talk) 05:29, 20 January 2009 (UTC)

pi calculation formula

${\frac {1}{\pi }}={\frac {2{\sqrt {2}}}{9801}}\sum _{k=0}^{\infty }{\frac {(4k)!(1103+26390k)}{(k!)^{4}396^{4k}}}\!$ i am a nineth grade student who is a bit ambitious. can some explain me this formula part by part?Harnithish (talk) 15:26, 18 January 2009 (UTC)

You may do better if you asked this question at the math desk. --Jayron32.talk.contribs 15:35, 18 January 2009 (UTC)

This formula was discovered by Srinivasa Ramanujan. I'm assuming you just want to know what the expression on the right hand side means rather than how the identity is proved (which is a much, much more difficult question !). Well, the $\sum _{k=0}^{\infty }$ part means "sum over the integer values of k starting at 0". Of course, we can't actually write down all the terms of this infinite sum, but we can write down as many as we have patience or time for. The $(4k)!$ means the factorial of 4k - the product of all the positive integers from 1 to 4k. And $(k)!^{4}$ is the fourth power of the factorial of k.

So the first term of the infinite sum, with k=0, is:

${\frac {(0)!\,(1103)}{(0!)^{4}\,396^{0}}}=1103$

because, by convention, 0! = 1. The second term, with k=1, is:

${\frac {(4)!\,(1103+26390)}{(1!)^{4}\,396^{4}}}={\frac {24\times 27493}{(396)^{4}}}$

and if we just stop with these two terms we have:

${\frac {2{\sqrt {2}}}{9801}}\,\left(1103+{\frac {24\times 27493}{(396)^{4}}}\right)=0.3183098862\cdots$

According to my calculator this is within 2x10^-11 of 1/π, so even with just two terms this is a very good approximation. Gandalf61 (talk) 17:21, 18 January 2009 (UTC)

A little algebra shows that the ratio of successive terms is asymptotically ${\frac {1}{99^{4}}}\left(1+O(k^{-1})\right)^{4}$, which I'm pretty sure means that every extra term you add gives you approximately 8 more decimal places of accuracy. Which is just further proof that Ramanujan had an amazing talent for generating formulas that seem to make no sense (and involve somewhat arbitrary-looking values) but do quite extraordinary things. Confusing Manifestation(Say hi!) 22:47, 18 January 2009 (UTC)

How was this formula derived? Genius notwithstanding, it seems unlikely that Ramanujan came up with the obscure and large numeric constants needed to make it work by "sheer insight." Was there a geometric or algebraic procedure that he used to convert some other pi identity form into this rapidly-converging form? Nimur (talk) 03:07, 20 January 2009 (UTC)

(Apparently so..., although I'm still not totally satisfied. More credit to Ramanujan's abilities, I suppose... Nimur (talk) 03:14, 20 January 2009 (UTC)

Certainly, if it hadn't come from Ramanujan, I'd have said it had to be bogus - but that guy certainly came out with a lot of very bizarre identities of this kind and I'm DEFINITELY not going to be the person who says he was wrong! SteveBaker (talk) 03:24, 20 January 2009 (UTC)

Long-term storage of lithium ion battery

I've read Lithium_ion_battery#Shelf_life, and it seems to suggest that I should store such batteries at refrigerator temps at a 40-60% charge. However, they won't stay at that charge, requiring me to periodically remove and recharge them (which will also heat them up). Is that better than just allowing them to fully discharge in the fridge ? These are backup batteries for cell phones, in case the primary batteries fail. Thus, I may not need them for several years. StuRat (talk) 17:10, 18 January 2009 (UTC)

Lithium-ion batteries should hold their charge for a long time. Self-discharge times are usually measured in years. If yours are not doing this then they are probably past their best. Here is a manufacturers' data sheet. Does not specifically say anything about periodically charging batteries in storage but I would say don't do it; each charge cycle shortens the batteries useful life and Li-ion batteries do not have the same problems that Ni-Cd and Pb-acid have with being left fully discharged. SpinningSpark 20:37, 18 January 2009 (UTC)

Muscle Tone and Protein Intake

Hello! I've heard that after strength-training exercises, it is important to eat something with a lot of protein immediately to foster muscle growth. Is there any truth to this? Does potential muscle growth significantly suffer if there is no immediate protein intake after a workout? If it is true, what qualifies as "immediate"? 30 minutes? 1 hour? 2 hours? There seems to be a lot of pseudoscience in the fitness community, so I was just wondering if this was a part of it. Thanks!--el Aprel (^facta-_facienda) 20:25, 18 January 2009 (UTC)

Well, yes and no. Eating protein doesn't automatically give you increased muscle tone: you need exercise for that. However, muscle is made of protein (among other things), so it only makes sense that in order to develop muscle tissue you'll need the raw materials to do it. You don't need to eat tons of protein for that though: a healthy, balanced diet will provide plenty of protein for that. The only rationale for an otherwise healthy person to eat much more protein (that I can think of off hand, at least) is if you also want to lose weight by eating fewer carbohydrates and proportionally increasing your protein intake. In summary: you need some protein to build muscle, but not tons of it, and not in the absence of exercise. – ClockworkSoul 22:43, 18 January 2009 (UTC)

These references are helpful: Dietary protein intake ... after endurance exercise and Postexercise protein intake. It is useful to eat protein immediately after exercise. I'm not aware of a study that examines the exact timing of the protein intake. Given that it will take a little time for the protein to be digested and absorbed, I guess that it would be best to eat the protein meal immediately after exercising. Axl ¤ [Talk] 23:06, 18 January 2009 (UTC)

Definitely yes. The post-workout meal is THE most important one, I read ("...except breakfast of course" it continue). Those who ate protein IMMEDIATELY post-workout got 33% more results, as I recall, than those just at regular mealtimes not near the exercise. Dont have time to google it maybe later I'll find the study. (I have no vested interest in protein shakes etc direct or indirect in case youre wondering)

Negritos, Indigenous Australians, Pacific Islanders, and Thai people...

Why is it that all of these people in my opinion have something about them which is similar to black Africans? It says that there's no definitive knowledge about the origin of Negritos but they are considered negroid, Indigenous Australians share many characteristics with negroes but some other things are different (noticably hair texture) and they also look a bit more mongoloid than pure African, and Pacific Islanders and people from Thailand do not look negroid yet they look more negroid than other obvious mongoloids (such as the Chinese, Koreans or Japanese) in my opinion.

Basically, is there any scientific evidence of a migration out of Africa for these population groups? It seems strange that they would develop similar traits independently.--Spring and Port Wine (talk) 21:39, 18 January 2009 (UTC)

In a sense, we all migrated out of Africa. However, I don't think that there are any closer connection than that between dark-skinned Africans and the other dark-skinned ethnic groups you list beyond the coincidence of dark skin. Also, don't read much into how people "look" as a test of genetic "closeness". Outward appearences mean little with regard to actual relatedness, and the outdated categories of "caucasoid" , "negroid" and "mongoloid" have little presence in modern science. --Jayron32.talk.contribs 22:05, 18 January 2009 (UTC)

Quite right. I live in the US and when the opportunity strikes, I like to say "We're all African Americans. Think about it.". ;) A Quest For Knowledge (talk) 15:07, 19 January 2009 (UTC)

If you accept the Recent African origin of modern humans, its unlikely they developed similar traits independently, rather their similar traits betray the shared origin of all humans. Rockpocket 22:25, 18 January 2009 (UTC)

I think the OP is asking whether the inhabitants of those regions migrated there without settling for a while at some other locale. In short, yes, genetic evidence suggests that the ethnicities you named may be part of a human migration that extended from Africa, along the coast to Southeastern Asia, and onward to Australia and the Pacific Islands. Take a look at early human migrations and prehistory of Australia for a bit more info. – ClockworkSoul 22:30, 18 January 2009 (UTC)

Indeed, see also Coastal Migration. Rockpocket 22:43, 18 January 2009 (UTC)

That map is way incomplete. What about cavemen who migrated from costal Europe to Newfoundland in North America 17,000 BP? ~AH1^(TCU) 01:27, 19 January 2009 (UTC)

I'm fairly certain that map is just meant to illustrate the inferences based on the haplotypes of the long-term inhabitants of various regions, and isn't actually supposed to describe every single migration event in the past 30,000 (give or take a few millenia) years. You might, however, be interested in models of migration to the New World. Note that it doesn't at any point make use the word "caveman". – ClockworkSoul 03:57, 19 January 2009 (UTC)

I don't have much experience with Thai people but from what little I've seen, Thai's aren't that dissimilar from other South East Asians like Malays for example, so I'm not particularly sure why you single them out... If anything, I would say they look more similar to Chinese, Koreans and Japanese. Nil Einne (talk) 19:31, 22 January 2009 (UTC)

A question and a few "if so..."s

Has the HIV genome been mapped? If so, has DNA microarray been performed to determine which transcripts are present at high levels in different stages? If so, is the information available online? 90.206.220.158 (talk) 21:58, 18 January 2009 (UTC)

And some answers...

• Has the HIV genome been mapped? Oh, yes. Here are three links to the complete reference genomes for:
  1. HIV1 (and 1286 more
  2. HIV2 (and 27 more)
  3. Simian-Human immunodeficiency virus (and 7 more)
• If so, has DNA microarray been performed to determine which transcripts are present at high levels in different stages? A search for "HIV microarray" over at PubMed [1] gives 194 hits, some of which are actually relevant. Here is an abstract of a very recent example of the application of microarrays to HIV infection.

Hope that's what you're looking for. – ClockworkSoul 22:11, 18 January 2009 (UTC)

wet vs. cold

does wet really feel different from cold, or is it an illusion? (we feel it's wet because we SEE that it is). —Preceding unsigned comment added by 82.120.227.136 (talk) 23:42, 18 January 2009 (UTC)

Well, considering that it's quite possible to be wet but not cold (warm or hot water, for instance) I'd say that they are indeed separate. Further, even when blindfolded I suspect you can reliably tell the difference between "cold" and "wet". This is science that is easy enough to test on your own (well, with someone else's help): blindfold the participant, then apply either a cold washrag from the freezer or a wet washrag to their hand and see if they can reliably determine which is which. -- 74.137.108.115 (talk) 00:02, 19 January 2009 (UTC)

In some cases, yes, you can certain tell. However, when bringing laundry in after its been hanging outside, I often find it difficult to tell if it's still wet or just cold. --Tango (talk) 00:15, 19 January 2009 (UTC)

Damp yes--but consider that a damp article of clothing probably behaves as if it were only cold. That is, the moisture is trapped in the material, so it will not "wet" a surface (or a hand testing its "wetness") but it will absorb heat (probably somewhat more effectively than the material alone). Even in this case, though, you are comparing "cold" to "wet and cold", not "cold" to "wet". -- 74.137.108.115 (talk) 00:46, 19 January 2009 (UTC)

The trouble is that both wet and cold things lower the temperature of your skin while it's in contact with it. The water in wet cloth conducts body heat away better than a dry cloth does - so in a very real sense, it IS cold as far as your skin is concerned. Worse still - dry-but-cold cloth could well become wet due to condensation of water out of the warm air surrounding your body...hence what was originally merely cold could become superficially moist to the touch. Obviously the degree of wetness and the degree of coldness of the cloth makes a difference to the feel - but whether you could judge that difference would depend on the exact conductivity and/or wetness of the cloth. However, because dry cloth will generally have a pretty low thermal conductivity - holding a piece of cold-but-dry cloth should warm it up to skin temperature pretty quickly...where you're unlikely to be able to dry out a piece of wet cloth very quickly by just holding it. So I think the trick should be to hold the cloth tightly in one hand for a few seconds and then see if it STILL feels cold to the touch with the other hand. This is only a theory - so do the experiment and let's see if we can do some new science. I want half of the Nobel prize money - but you can go to Stockholm to collect it. :-) SteveBaker (talk) 00:50, 19 January 2009 (UTC)

What Steve should have said is that its only a hypothesis, and you should do the experiment to test it. A theory being something entirely different than what he describes above. OK. I'm done being a pedantic asshole for the day. Back to your regularly scheduled discussion. --Jayron32.talk.contribs 01:44, 19 January 2009 (UTC)

Indeed - Steve should know better... shame on you! ;) --Tango (talk) 02:11, 19 January 2009 (UTC)

Yeah! If anyone should get the Nobel prize it is you two (in Literature) for your valuable refutation of Steve's word choice. —Preceding unsigned comment added by 82.120.227.136 (talk) 12:00, 19 January 2009 (UTC)

Damn! Obviously you're going to make me turn in my magic decoder ring - but do I get to keep the lab coat? SteveBaker (talk) 15:53, 19 January 2009 (UTC)

Well, we'll let you stay in the scientist club for now, but there will be a demerit on your permanent record! --Jayron32.talk.contribs 18:48, 19 January 2009 (UTC)

I'm not sure Steve's experiment would work very well anyway. I often get puzzled with whether my drying is still damp or merely chilly and the squeeze test doesn't work well for me. Cloth is typically a good insulator, so it really doesn't warm up in a significant way. What I typically do is examine the rest of the load. Since it's unlikely to dry in a uniform way, a load that's damp will probably have a wet piece in there somewhere (rolled sock, folded cuff, etc). In fact, a rolled sock or other lump can be useful from the outset; being more insulated, it stays damp the longest, but also takes longer to chill down to ambient temperature. Matt Deres (talk) 19:06, 19 January 2009 (UTC)

I good insulator should warm up quicker, since you only have to warm up the part in immeadiate contact

My thoughthypothesis exactly. If it's just cold then the thermal mass of (say) the first millimeter of depth of the cloth is tiny and should warm up quickly (while your hand senses it as cold). The heat won't be conducted away into the body of the cloth because it's such a good insulator - so the surface of the cloth will get warm. To contrast, wet cloth will conduct the heat from your hand away without getting significantly warmer - and it'll continue to do that until it finally dries out. Hence, if you warm it up with one hand - then switch to the other hand to measure the resulting temperature, you should get a feeling which is actually the opposite of the truth: If your 'measurement' hand still feels that the cloth is cold - then it's wet (it might be cold AND wet), but if your 'measurement' hand says that the cloth now feels warmer than it did before - then the cloth was definitely not wet - but merely cold. That's the hypothesis - now we need to proceed to the experiment - after which we may publish the results in the well known peer-reviewed "Wash-day journal of thermodynamics and biosensing". If others can repeat the experiment successfully then it will become a Theory (big 'T') and the Nobel prize will surely follow. SteveBaker (talk) 13:58, 20 January 2009 (UTC)

(ahem) Getting back to the original question, I was wondering how the sense of touch works when it comes to non-solid objects. Is it only because of the substance's behavior and our feeling its movement that we know it is "wet", or is there some intrinsic property of our sense of touch which determines the "wetness" or "dampness" of a subject? So I guess I haven't answered anything, but instead added a new question.-RunningOnBrains 18:57, 19 January 2009 (UTC)

I believe surface tension has something to do with it, a liquid with very high surface tension (mercury, say) won't feel as wet as something with a lower surface tension (water or oil, say). I haven't spent much time handling mercury, though, so I'm not entirely sure that's right. --Tango (talk) 19:07, 19 January 2009 (UTC)

My recollection of handling mercury (and that was 35 years ago) was that it doesn't feel wet...but to be honest, your senses are too busy saying "This is unreasonably heavy for a liquid" for you to notice much else. It's a good conductor of heat - so it ought to feel cold - but it also doesn't "wet" the surface of your hand - so even as you move it around, you don't have a wet hand. It's really weird stuff when you actually get to play with it. SteveBaker (talk) 20:40, 19 January 2009 (UTC)

That fits with my understanding of the theory. We should probably point out at this point that mercury is toxic and it is unwise to play with it in the manner described by Steve. --Tango (talk) 20:53, 19 January 2009 (UTC)

I can't remember exactly where I heard/read about it, but I recall a science program/article that discussed the issue. According to the program, it seems that we do not have "wet" touch receptors. The sensation of "wet" is actually caused by the joint triggering of "cold" and "pressure" receptors in our skin. This was then demonstrated by the host being blindfolded, and having the skin pressed lightly by a cold object. The blindfolded host remarked that the object felt "wet". Just pressure or just cold isn't enough to get the "wet" feeling - it's a combination of cold and pressure which does it. -- 128.104.112.113 (talk) 22:51, 19 January 2009 (UTC)

Which returns us to the question of warm and hot liquids--do they not feel "wet" then? And why would mercury, which possesses (and presumably excels in) those two criteria be "less wet" than water?

I suspect that some part of the determination rests on friction--if the "unknown material" slides easily across the skin then "wet" would be indicated. If the material applies signficant friction or resists movement across the skin than "wet" would be counterindicated. This is, however, only speculation. -- 74.137.108.115 (talk) 04:08, 20 January 2009 (UTC)

After somewhat extensive review in Cognitive psychology, Perception, Somatosensory system, and Mechanoreceptor I believe I better understand how the brain determines the sensation "wet". The simplistic introductory explanation that touch consists of hot, cold, pain and pressure neglects the further subdivision of the "pressure" receptors. From Mechanoreceptor, they are:

Ruffini's end organ detects sustained pressure.
Meissner's corpuscle detects changes in texture (vibrations around 50 Hz); adapts rapidly.
Pacinian corpuscle detects deep pressure and rapid vibrations (about 200-300 Hz).
Merkel's disc detects sustained touch and pressure.
Mechanorecepting Free nerve endings ((touch, pressure, stretch)
Hair follicle receptors are located in hair follicles and sense the position of hairs.

This gives us many combinations of "pressure" sensory input, some of which are most likely identified as "wet" by our brain. Several possibile indicators are:

• "wet" substances distribute pressure more evenly
• "wet" substances don't cause significant friction (stretching of the skin)
• "wet" substances have internal fluid flows that can be detected (through vibration, texture or motion of hair follicles)
• "wet" substances expand predictably on the skin (wetting the surface)
• "wet" substances do not force uniform motion

Undoubtedly there are other inputs that may suggest "wet" (temperature and temperature differential, sight, sound, etc.) but the exclusion of those inputs does not seem to eliminate the ability to perceive "wet" (though accuracy may be reduced). It's amazing the amount of complexity that goes into a simple evaluation of "wetness". -- 74.137.108.115 (talk) 06:20, 20 January 2009 (UTC)

Fascinating information! Thanks!

So now we know that there isn't some kind of special 'wetness' sensor (I didn't think there could be because the sensing organs themselves have to be under the layer of skin cells - so they would be out of contact with the water anyway).

But everyday experience says that we have an incredibly hard time telling the difference between "cold" and "wet" - anyone who put laundry out to dry outdoors on a chilly day will attest to that. You go out to grab your clothes and you simply can't tell whether they are dry-yet-cold or still wet. The theoryhypothesis that various forms of pressure/friction/stretch are giving you wetness cues seems to be busted by that simple, familiar, experiment. The alternate hypothesis (that the 'cold' receptor predicts wetness by estimating thermal conductivity) is entirely born out by that experience. It's possible that some of these other mechanisms provide backup information - but the sensation of cold clearly overrides anything that's saying "No! It must be dry because it's not slippery enough". We feel "cold" and our brain says "wet". QED.

SteveBaker (talk) 20:42, 20 January 2009 (UTC)

Which, again, completely ignores that something can be "wet" without being "cold". I'm not saying that "cold" doesn't play an important role in determining wetness (or, more appropriately for your example, dampness); but it cannot be a uniquely-determining factor. Also consider that "damp" but not "wet" laundry probably does not exhibit the potential indicators of wetness as described above (the cloth having a greater affinty for the water than skin would), so in that case you would be relying on primarily "cold" information. The next time you have an ambiguously cold/"damp" cloth, try putting it under running water for a few moments and then see if you can tell a difference between "damp" and "wet" (and "cold"). From my personal experience, every "cold" object does not feel "wet" or "damp". Perhaps in your laundry example your brain expects to feel "damp" and ends up misinterpreting "cold". -- 74.137.108.115 (talk) 21:41, 20 January 2009 (UTC)

I don't know whether this anecdone will help. I used to live in Malaysia. There it's usually relatively easy to tell if your clothes are damp or not. Here in NZ particularly in winter, I find it rather difficult to tell whether my clothes are damp, or simply cold. As SB says, there are definitely other sensations that come into play, including the sensation related to friction and stuff of wet objects and likely including visual, but I do think cold is a very big factor in determing wetness. Bear in mind it's unlikely to be simply cold per se, but in precisely how it feels cold, i.e. that it quickly conducts heat away from your body so feels cold rather quickly Nil Einne (talk) 19:41, 22 January 2009 (UTC)

leaded brass

Is it safe to handle leaded brass? I made a paperweight out of machine shop brass. Do I need to wash my hands if I handle it? --VectorField (talk) 23:56, 18 January 2009 (UTC)

Lead isn't so toxic that just handling it is harmful, you would generally have to eat it, drink it, or inhale it. And only a small portion of leaded brass is lead. The other main ingredients are copper and zinc, neither of which is dangerous to handle. I suppose you might as well wash your hands, though, why not ? The only likely danger I could see is inhaling fumes when you first made it. StuRat (talk) 00:39, 19 January 2009 (UTC)

I also wonder whether the lead is forming an amalgam with the zinc and copper - in which case it ought to be OK. For the longest time, dentists have been filling teeth with an amalgam of silver and the oh-so-very-toxic mercury - so long as it remains as an amalgam it's pretty safe. SteveBaker (talk) 00:52, 19 January 2009 (UTC)

It might be wise to wash your hands before you eat if you've been handling it, but unless you suck your thumb, that's the only way you're likely to get much lead into your system from touching it. Even then, it will be minute amounts. --Tango (talk) 01:15, 19 January 2009 (UTC)

As noted, its probably entirely safe to handle it, but its probably not a good idea to eat or drink off of it. As long as you are not regularly ingesting things which are in contact with it, you are likely fine. Most of the problems with lead comes from lead-containing compounds, such as tetraethyl lead and lead paint, which are soluble in body tissues and much easier to ingest into the body. Metallic lead, or lead-containing alloys are much less of a threat; you can get lead poising my directly ingesting lead or inhaling powdered metallic lead, but the threat is MUCH less than from lead-based compounds. See Lead poisoning for more info. --Jayron32.talk.contribs 01:42, 19 January 2009 (UTC)

Always wash your hands before putting them in your (or anyone else's) mouth or handling food.--GreenSpigot (talk) 02:03, 19 January 2009 (UTC)

Despite statements above of what lead use is safe, U.S. standards for lead in consumer products are being sharply cut starting February 2009 by the Consumer Product Safety Improvement Act. The exposure level for surface coatings on a wide array of products, especially those intended for children, drops to 600 ppm 10 February 2009, then down to 300 ppm on 14 August 2009, then down to 100 ppm 14 August 2011, with certificates of testing by certified labs which do not exist yet in sufficient numbers. This is partly because of toys made in China with lead paint, and also because a metal charm on a shoe was lead and may have killed the child who swallowed it. In general, lead-containing objects should be kept out of the reach of children. No more toy lead soldiers. Edison (talk) 19:50, 19 January 2009 (UTC)

I believe we did say that the danger from lead comes from ingesting it, not touching it. I have a hard time imagining a child swallowing a paper-weight, unless it's far smaller than I'm thinking. I suppose they might lick it, though, so keep it away from small children. As for tightening up the lead requirements, that seems to rather miss the mark, as toys from China which don't adhere to our current standards are the real problem. StuRat (talk) 20:18, 19 January 2009 (UTC)

How so? According to Edison and the article, the new standards impose new testing and documentation requirements. Also are you sure all those toys from China don't adhere to the current standards? Some of them may it's just that the manufacturers realised sellng toys with any appreciable quantity of lead is not good business sense. Nil Einne (talk) 20:05, 22 January 2009 (UTC)

If "new testing and documentation requirements" means they will actually enforce the current standards, then that's good. I found a source which says that 54 toys were found which exceed the 600 PPM standard: [2]. The American Academy of Pediatricians recommends a level of only 40 PPM, so I've changed my opinion, they need to lower the amount allowed in toys even more AND they need to enforce the law. StuRat (talk) 20:52, 22 January 2009 (UTC)

Most lead soldiers were actually made of a lead/tin alloy and painted or enameled - so the amount of lead getting out to the children was much less than some people think. Early pure-lead soldiers were so fragile that intact examples are now exceedingly rare collectors items. Of course in those early days, the 'lead' in pencils was really lead... SteveBaker (talk) 20:01, 19 January 2009 (UTC)

Except that ignores how lovely it was to bite the soft lead toys... My grandparents held on to some old toys for us to play with when we visited; none of the lead farm-people in the farm animal box had feet, some were missing heads. There were little toothmarks on the ends. 79.66.92.148 (talk) 21:48, 19 January 2009 (UTC)

The classic British guardsmen that I have (given to me by my father from when he was a kid) had all lost their heads. When I got them the heads were held on by plasticine stuffed into head and body with a matchstick pushed through both. I didn't see any tooth-marks though. I was able to clean them up and flow some solder into the lead to fix them up like new. This probably destroyed any antique value they may ever have had - but they look nice. SteveBaker (talk) 23:18, 19 January 2009 (UTC)

Perhaps you could make everyone happy by shining up your paperweight one last time, then giving it a light coat of spray sealant (polyurethane, etc). --DaHorsesMouth (talk) 03:06, 20 January 2009 (UTC)

What? How old are these lead soldiers? It's questionable if real lead was ever used in pencils. According to our article on pencil, a pure deposit of graphite was discovered sometime in the 1500s (even if it was thought to be lead) which had to be covered by something (often sheep skin or string) because it was too soft to simply hold. Eventually the Italians thought of using wood. The Germans and later the French, Austrians and potentially Americans managed to use powdered graphite (the French had to since the English had/have the only source of naturally occuring known suitably pure graphite in the world and they were at war). While lead was used in styluses by the ancient Egyptians, it's questionable IMHO if these can be called pencils sine they share virtually none of the characteristics. Nil Einne (talk) 20:00, 22 January 2009 (UTC)