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John Cuthber

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Posts posted by John Cuthber

  1. Expanding gases generally get cold but he was talking about boiling points. The heat of vaporisation is a lot bigger than the cooling effect of expansion for most cases.

    Running oxygen into the air intake would be interesting. With a 1 litre displacement engine running at 1000 rpm you would need something like 5l/m of oxygen to raise the concentration by 1%. How much oxygen does a typical cylinder hold?

  2. "I don't really think that would be a main reason why NO2 is used, because the boiling temperature of NO2 is higher than that of O2. So if the idea was to get the mixture denser to get more into the engine, then using O2 would be the better choice."

    No, it wouldn't.

    You can liquefy N2O (the stuff we are actually talking about, rather than NO2) at room temperature by compressing it into a cylinder. You can't do that with oxygen. To liquefy oxygen you also have to cool it. If you used liquid oxygen then the temperature would be so low that the fuel wouldn't vapourise. At best it wouldn't work. At worst you would briefly have an explosive mush then no car...

  3. I realise it's not the same thing, but at work I regularly use plastic pipe at 5000 PSI (yes, I mean over 300 bar)- it works fine. We also have copper "domestic" pipes which are being attacked by the soft water.

    The pipes that feed water to my washing machine at home are some flexible rubber/ plastic stuff and stand up to the pressure of the cold water mains perfectly well.

  4. OK, sorry I didn't read your post correctly. There are no intermolecular forces in a molecule (heroin or anything else). How can you have forces "between one molecule"? It's like the sound of one hand clapping.


    If you are talking about the bonding between heroin molecules in a crystal then I think the dipole-dipole interactions will dominate.

  5. Part of the reason NO2 works (or so I read) is that it cools the gas mixture going into the engine (because it's cold having just evaporated from the liquid in the cylinder). The cold gas going in is denser so it holds a greater mass of fuel and oxidiser in each volume. With the engine sweeping out a given volume (the displacement) you get more fuel and oxidiser per stroke with cold gas. That's where a lot of the power gain comes from. The energy of decomposition of the NO2 helps and so does the greater effective oxygen concentration.

  6. Cyanide certainly hydrolyses in water so it will go away eventually, even without outside help. Also, while it is very toxic there are biological mechanisms for detoxification.

    Hydrogen cyanide is volatile and will disperse into the atmosphere by evaporation; once in the air it will be destroyed by the same sort of mechanisms that degrade other organic matter in the air..

    Not sure how much this helps but it might give you an idea where to look.

  7. Form swansnot "Your statement, that physics has an insolvable problem, implies chemistry has none"

    No; it implies that, unless you are prepared make approximations, you never get anywhere. Belittling chemistry as just an approximation is pointless because approximations are all you get.


    Also, if you want to argue by authority A la "stamp collecting" comment, pick someone who didn't go on to do things like this."In 1933, four years before his death, Ernest Rutherford said that people who thought his discoveries would lead to nuclear power were talking moonshine." or say "X-rays will prove to be a hoax." or that the earth was only 20 million years old.


    Having said that, I quite agree with you that a heavy dose of sarcasm does a good job at getting rid of people who simply refuse to accept the laws of physics. That's not prejudice by physicists; that's just prejudice against fools.

  8. Ammonium hydroxide is a myth; it might exist under some weird low temp/ high pressure conditions.

    Ammonia dissolves in water; the product is known by various names. Aqueous ammonia and ammonia water are 2 of the common ones.


    If I try to make ammonium hydroxide by, for example reacting sodium hydroxide with ammonium chloride in solution nothing much should happen. I should get a solution containing ammonium ions sodium ions chloride ions and hydroxide ions. (certainly, if I do this with potassium chloride and sodium hydroxide in solution nothing happens unless the concentrations are so high that salt doesn't dissolve in water)

    In the real world the mixture gets warm and gives off ammonia. This is because the ammonium ion is a relatively strong acid and the hydroxide ion is a strong base; they cannot co exist (certainly not at any meaningful concentration) because they react with eachother. The proton hops across from the NH4+ to the OH- and gives ammonia and water.


    The misleading nomenclature persists, partly for historical reasons (ie "we always called it that") and mainly because it sounds better to say 14% ammonium hydroxide than (roughly) 7 % ammonia. See, it's a bigger number so it sells better.

    If ammonium hydroxide existed it would have a molecular weight of 35.

    A 14 M solution would have 14*35 ie 490g of "ammonium hydroxide" but would really just have 14*17 ie 238 g of ammonia per litre.

    It's the same stuff but it looks like it's 49% (w/v) rather than 23.8%(w/v).

    Find me some data on the N O distance in NH4OH and I will think about believing in it; otherwise, since this is a scientific site, lets try to stamp it out.

  9. I just wonder, has anyone here changed their opinion on any of the matters that have been debated as a result of what they have read?


    "Originally Posted by John Cuthber

    I think you have missed the point; I shouldn't have to move to make way for the smokers. It should be the other way round. They are the ones doing something offensive; not me.

    You don't have to move. You choose to. I don't have to move away from fat people with rotten teeth, but I choose to because it's gross - even though they're the ones being offensive."


    The problem is that they think it's reasonable to sit near me and light up. Also, while from my point of view it's a choice, but from the point of view of some asthmatics these smokers make places like bus stations no-go areas.

    I still mainatin that the people doing something odd have the responsibillity to ensure that it does not adversely impact on others. It is not the responsibillity of everyone else to pander to them.



    The thing is, when a smoking area is deamed as such - by the owner of the business, then what right do we have to make laws to stop that? Just like a home owner, you don't have a right to tell them what to do in their own business. If you don't like my smoking in my house, then don't come in. Same with business. If you don't like them allowing smoking and you don't want to be around it, then don't come in.


    Same problem; I got there first but they lit up anyway.


    This isn't about your right to frequent any business you want without being offended - you don't have that right. Just like you don't have a right to walk in anybody's house and not be offended.

    Do you really not think that there's a difference?

    I can walk around my house naked; I can't do that in a shop, even if I own it.


    It is paid for by them and they have a right to allow smoking or slow emition of mustard gas too - in my opinion - so long as it is marked and partitioned appropriately.


    How many times do I have to point out that the partitioning does not, in my experience, work?


    You don't have a right to enforce your ideas of offensive behavior on everyone else. "

    No, I don't, but society does. Here in the UK it has made that decision.


    BTW, Pangloss,


    "Carbon monoxide kills in sufficient quantity. Do not drive your car past my house anymore. You don't know that it won't harm me."

    No problem; I don't drive. Carbon dioxide is also toxic...

  10. Well, as a chemist I have, from time to time, heard arrogant physicists saying that physics is the only real science; the others are derived from it or are approximations. I usually ask them if they have solved the 3 body problem yet.

    BTW, am I the only one who wonders what GutZ will do when he grows up?

  11. Since I can deem the tap to dispense whatever I want I will have it dispense 10%v/v alcohol. Not only does that mean that to get 9 pints of water all I have to do is fill the 10 pint jug (OK there's something else there too, but it's 9 pints of water.), but I can get pleasntly pickled later on and start thinking about numerology.

  12. There seem to be several debates going on here.

    Should we ban smoking in public?

    Is there evidence of harm from second hand smoke?

    Is there evidence of harm from very short exposures.


    Well, here's my 2d worth

    Pangloss, when you say "

    I think you know better than that. I have no problem with your objections to noxious odor and discourteous behavior, by the way. By all means, object on that basis. I support your right to take your business elsewhere, 100%." I think you have missed the point; I shouldn't have to move to make way for the smokers. It should be the other way round. They are the ones doing something offensive; not me.


    OK, I know that the health risk from someone elses smoke is not huge; there are studies that show evidence of harm and it is scientificly reasonable to make an argument like this

    Smokers are known to have high rates of cancer.

    While this may be due to some other effect (perhaps the lighters or matches are the problem) it is reasonable to say that smoke causes cancer in smokers.

    Unless someone can explain how the smoke "knows" that is is in the lungs of the person who lit the cig then it is reasonable to assume that smoke will cause cancer in non smokers too.

    There may be a cutoff point below which there is no effect but there would need to be a mechanism proposed that "turns off" the carcinogenicity at low levels. AFAIK there is no such mechanism so I do not believe that there is a "safe" exposure. There may well be a level where, compared to the other risks in life, the risks from second hand smoke are negligible. I don't know what that level is. It will certainly depend on other things.

    This makes it look like any smoke is "harming me a little bit" by raising my risk of cancer (and where I have written cancer there are other health problems to which the same logic applies).

    There is also the question of the fact that smoke stinks. When someone farts in a lift nobody bothers to complain about hydrogen sulphide toxicity. It's simply not socially acceptable; proof of physical harm doesn't eneter into it.


    On the other hand I'm not sure I agree with the statement that it's not OK to harm me a little bit. OK, I realise that seems odd, but I know that the kids next door make a lot of noise and it annoys me; that probably raises my blood pressure and therefore in some (tiny) way it is detrimental to my health. I also know that the parties I host from time to time do exactly the same to my neighbours.

    Neither of us sues the other for damages because we both know

    (1) we are as guilty as each other and

    (2) we wouldn't get anywhere; the jury would decide that noisy kids or the odd party are reasonable things to put up with. If I were hosting parties every week that might be another matter. In particular I could get taken to court over it and fined (or even jailed if I carried on) for causing a nuisance.


    Whether or not having to put up with other people's smoke is "reasonable" or not is a decision made by society as a whole. At least in principle, in a democracy that's where the laws come from.

    Society here in the UK seems to have decided that, while it was acceptable to smoke in public in the past, it is no longer acceptable.

    OK the laws are not a perfect reflection of societies view- they cannot be since different people have different views but we chose governments and thereby we choose laws. If we don't like it it's our own fault (please don't turn this thread into a "the legal system doesn't work because... debate. I know it doesn't so feel free to start another thread about it)


    OK that's why theres a law coming in about smoking in the UK.

    Now can we get back to the question of whether or not it is scientifically valid to clain that short exposures to second hand smoke are a health risk?

    How would you construct the experiment to answer that question and would it be possible to perform the experiment?

    Alternatively, is there a valid theory that gives rise to a mechanism for such an effect.

    I think there might be in principle. It's the old idea that "it only takes one cancerous cell to grow into a cancer and it only takes one carcinogenic molecule to turn a cell cancerous because there's only 1 (nuclear) DNA molecule in a cell for it to interact with". I'm not at all sure about the second clause there.

  13. How do you interpret Insane alien's comment that "they cause hayfever. histamines are nasty and toturous" without thinking that someone claimed "hayfever is caused by histamine "? or do you accept that it may be a FACT that the claim was made?

    Another reasonable hypothesis (albeit not really a FACT) is that if the histamine response didn't do more good than harm evolution would have dumped it long ago.

  14. This debate has gone on a lot longer tha I thought it would.

    As I see it, if people want to smoke then let them. On the other hand the assumption shoulkd be that places should be smoke free unless otherwise specified. There needs to be a good reason to let people blow toxic fumes at other people and "because I want to" isn't an adequate reason.

    I have yet to see a pub with an adequate segragation of smoking and non smoking areas- you can still smell the smoke in the non smoking rooms.

    Why should a selfish group of people be permitted to polute any area they chose; surely the default state should be smoke free and only specified areas set aside for smoking? Since these areas, as far as I have seen, cannot be in the same building as non smoking areas they need to be entirely separate or outside.

  15. There are plenty of full-scale electricity generating stations that run on methane. At the moment it is natural gas but, if the price of methane from, for example, sewage or landfill gas, became cheap and plentiful they could easilly use that. A search on "biogas" will give you more info.

  16. The idea that, because antihistamines relieve (some of) the symptoms of hayfever, it follows that hayfever is caused by histamine doesn't quite wrok.


    I woke up this morning with a headache and I took a couple of asprins. They made the headache go away. The headache was not caused by a shortage of asprin; it was due to too much whiskey last night.

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