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John Cuthber

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Posts posted by John Cuthber


  1. "How can I tell if a particular bored is made of Gold or something less valuable like copper?"

    Gold is golden in colour whereas copper is copper coloured.

    The gold plating is very thin If you are setting up a "collection of the elements" then old circuit boards are one of the few places you will get gold for free.


  2. Part of the problm for making a hexanitrobenzene is that each nitro group you add removes electrons from the ring and makes it more difficult for the next substitution to happen.

    It's possible to add methyl groups to a benzene ring using chloromethane (or, more practically iodomethane) and a lewis acid catalyst like AlCl3.

    If you do this you tend to get more than one methyl on each ring because the methyl benzene is more reactive than benzene itself and, similarly the dimethyl benzenes are more reactive still. Getting all 6 to react isn't as easy as it looks because of steric effects.


  3. Most of the alphas just crash into the Bi and are slowed down, pick up a couple of electrons and are converted to He gas.

    A tiny percentage are caught by the Bi nuclei and form 210At.

    That At will, in time decay largely by electron capture (and give off a gamma ray) Partly by alpha emmission.

    Of course, that all depends on having 206Bi to start with and, since it has a rather short half life (about 15 days), you almost certainly don't have any.

    I doubt that the relatively stable 209Bi traps alphas to any great extent - not least because it's a (very weak) alpha emmiter.

    Overall, I'm not sure what budullewraagh is talking about.


  4. I guess he wants to know why, unlike most indicators, starch is added near the end of the titration. The fact that this is true for thousands of titrations doesn't really matter.

     

    Anyway there are several reasons.

    Starch is a reducing agent (especially if it hydrolyses to glucose) so you don't want to add it too soon or it may react with the oxidant and upset the result.

    More importantly when the starch reacts with a large excess of iodine it tends to "trap" some of the iodine so, even after enough thiosulphate has been addded, the mixture stays blue for a while and you tend to add too much thiosulphate. This spoils the accuracy of the titration.


  5. If I get a piece of glass rod and clamp it vertically, (held at the top) then heat it in the middle eventually, when the glass melts, it will snap in 2 under its own weight.

    I bet that's not what "hello help100" had in mind, but it does show that the temperature may have an effect.

     

    My guess is that he's on about shattering glass by heating it quickly. The problem is that taking ordinary glass and quencing it in liquid nitrogen will shatter it too. You could say that it breaks at roughly minus two hundred degrees.

    With some types of glass like fused quartz it's practically impossible to shatter them this way. With other glasses it's quite easy.


  6. I thought the body's acetate pool was turned over pretty fast.

    Anyway, measuring traces of formaldehyde in beer would be easy enough in a lab but (at least as far as I can see) rather difficult at home.

    I can't see why on earth anyone would add something to their product that would make people like it less. Beer doesn't go off so long as you keep the dirt out of it so I can't see HCHO as a preservative- you would need quite a lot anyway and the stuff would be undrinkable.

    What's your friend's evidence for the addition of formaldehyde to beer?


  7. I don't see what the big deal is.

    Mathematically 0.001 is the same as 1/1000,

    so 0.001 M is the same as 1/1000 M

    Since multiplication gives the same answer whichever way round you do it 1/1000 M is the same as M X 1/1000.

    Multiplication by 1 does nothing so you can leave it out and get M/1000


  8. Al is relatively transparent to X rays.

    Thin layers of Al are transparent to ordinary light (and are used as beamsplitting mirrors).

    Al2O3 (corundum, btw; carborundum is SiC) is transparent to, not just visible light, but quite a long way into the UV and IR as well.

    I will be impressed by the plasic with a better strength to weight ratio at say, 400C.

    What was the original question meant to mean?


  9. Gallium and tin are probably the 2 commonest (after water) things that expand on freezing. The answer involves the lattice formed from water, being held together by relatively weak hydrogen bonds, has quite big gaps between the molecules. When it melts the molecules can slip into those gaps.(And I'm afraid I haven't a clue why Ga and Sn do this, it may be related to the fact that they have unusually long liquid ranges)


  10. What are you on about?

    Ever heard of a high pressure mercury lamp?

    They have relatively large amounts of mercury in them and they work quite well at producing UV light.

    Anyway, as has been said, the little Hg in an ordinary lamp isn't a problem. If it's an old enough lamp then the Be in the phosphor might be.


  11. OK, It's been a while so I apologise for bumping this but... If this quote about Lister

    "He also made surgeons wear clean gloves and wash their hands before and after operations with 5% carbolic acid solutions. Although it should be noted that he first persuaded Robert Goodyear to manufacture rubber gloves for his nurse since the carbolic acid caused her to suffer from contact dermatitis. Instruments were also washed in the same solution and assistants sprayed the solution in the operating theatre. One of his conclusions was to stop using natural porous materials in manufacturing the handles of medical instruments."

    from wiki is right then Lister was using 5% phenol, that's 50g/litre. Last time I checked 50,000mg/L was not 5 times as concentrated as 100 mg/L. I apologise for underestimating the difference- the stuff Noty was talking about is 500 times more dilute.


  12. I think that procedure probably gives reasonably clean nucleic acid- certainly if there were a lot of trash in it, it wouldn't be a stringy goo like DNA.

    I think it's not too dificult to hydrlyse DNA to its constituents. Enzymatic hydrolysis would be neatest but I think a strong base would do.


  13. IIRC the carbolic acid that Lister used in the pioneering days of antisepsis was 1% phenol ie about 100 times more concentrated than the solution you are using. Since his patients (and the doctors) survived spraying it around, I think it's fair to say that you don't need to worry too much.

    Of course, as with all toxic chemicals, it's prudent to keep exposure low.


  14. "I wonder if alot of these animals generally seek shelter when they hear low frequency sound, as associated with thunderstorms, and this helps them deal with earthquakes by coincidence."

    If you are a cow and there is a thunderstorm you are in trouble. You can't rely on going into a nice steel framed building (certainly across evolutionary timescales you can't) and you don't really want to stand under a tree. If there's a wood then going into it and hoping you aren't under the tree that gets hit would be good. Going down hill would also be better than uphill.

     

    If you are a cow that knows an earthquake is comming your best bet is to stand in the open (so nothing lands on you); this would be sucidal in a thunderstorm. If it's going to create a tsunami then you really want to go up hill rather than down.

    The behaviour that would be adaptive for (relatively common) thunderstorms would be ill advised if there's a (relatively rare) earthquake.

     

    Btw, what's all this rubbish about 5 senses? You can close your eyes and touch your nose with your index finger. You cant hear, see, taste smell or feel it coming- how can you do this?

    How do you know when your bladder is full or when you are hungry?

    People have a lot more than 5 senses.

    It's entirely reasonable that cattle and other animals sense the oncoming earthquake. It's also possible that after an earthquake people think "That's odd, my dog was acting strange just before the quake; he must have known it was comming." Of course, the dog might have known that next door's bitch was on heat. Coincidences like that keep the psycics and astrologers in business.

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