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John Cuthber

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Everything posted by John Cuthber

  1. Actually, to be a bit more specific, silver nitrate reacts with chloride rather than chlorine. Since Cl2 dissociates in water to give chloride it is true to say that silver nitrate will give a ppt with a solution of chlorine. On the other hand, if you wait a while for the chlorine to difuse out of the water (or better yet, bubble air through it) then test with silver nitrate you will still get a ppt. It won't tell you if the chlorine has gone. It would, for example give a really strong positive test with seawater but that has essentially no free chlorine. Measuring free chlorine is a bit more tricky I think there are kits to do this; sold to aquarium owners. If I wanted to dechlorinate water for an aquarium I'd probably just put pondweed of some sort in it and wait for a day or so. The plants might take a bit of a hammering but it would save the fish.
  2. There are techniques using RF to identify chemicals- NMR is a case in point and the 21cm line from hydrogen is much used in astronomy. On the other hand it's rather difficult to get decent sensitivity because the energy level differences are small so thermal effects tend to wash out the spectra.
  3. I have to aagree with bignose; "Statistics isn't science." is one of the best jokes I have seen in a while. Not only is it clearly out of place in this topic where the temperature of the earth is being discussed (Temperature in the arctic or the tropics; Perhaps the London weather centre- OK Summer or Winter?- best take some sort of average) but the fundamental role of statistics in modern physice makes it a staggeringly ill thought out comment. Stats can only be used to lie to people who don't understand it; OK that's quite a big part of the general population but most of us are big girls and boys; quite grown up and quite clever. I can't see it working here; anyone posting bad maths on this site will just get laughed at.
  4. All this talk of war puzzles me. What countries have declared war? Who's soldiers are we talking about? Terrorist is just a label for someone doing something criminal; mass murder to make a political point is still mass murder and should be treated as such. Since there isn't a war these people should be treated as civilian criminal suspects and given a fair trial. Since the US government has already made up its mind about them it's difficult to see them getting a fair trial under US jurisdiction so they ought to be tried elsewhere; ironically China might be as good as anywhere.
  5. The statement "they also know that people who are circumcised are easier to use mind control over " would make sense if people thought with their foreskins. While a very similar assertion has been made many times about men in general, it has never been remotely close to true. There's also the glitch concerning banking families among the elite. It may sound anti semitic to say that a lot of banking families are Jewish (and therefore circumcised); actually there's nothing prejudiced about simply making that observation. It probably stems from a Christian belief that any form of money lending was usury and hence banned. That's just one bit of evidence. That's all I need to falsify a theory. Here's a second bit of evidence. If all the glue failed today we would notice- the postal system would grind to a messy halt. Sorry to be the bearer of bad news but your own "predictions", by failing to come true, are sufficient to prove that you are simply wrong. Much earlier in the thread you asked why this should not be counted as speculation. Well now we have an answer; this is a scientific website and, as such, we only have to consider speculation of a broadly scientific nature. Science makes theories; from those it makes predictions; if they don't turn out to be true then it's time to ditch the theory..
  6. According to the wiki article on albinism about 1 in 70 of us has at least one gene for albinism. That means that over 98% of us don't. That's totally incompatible with the idea that all white people descended from albinos. The idea simply doesn't stand up.
  7. In order to sense the outside world the sense organs have to be on the outside of the body (at least, they can't be stuck in the middle). All cells produce waste so they have to get rid of it somehow. For those cells near the surface they might as well just dump it. However; earwax, saliva, snot and tears are not waste products. They are deliberately produced to help keep the sense organs clean. Sweat too has a real function as well as dumping some waste.
  8. Yes, bleach, strong acids or bases, phenol or just plain heat will all kill bacteria through mechanisms that are difficult to "evolve around". Unfortunately they also kill human cells so they cannot be used in the same way as antibiotics. The problem is that human cells and bacteria are rather similar so there aren't many ways to get selective toxicity. To get that selectivity you need to exploit relatively subtle aspects of the bacteria and those are the subtle things the bacteria can find ways to work round. (BTW, there's a big difference between antibodies and antibiotics.)
  9. If the temperature change is big then you certainly can't use the ideal gas laws. You might find tables of this sort of data somewhere on the net, but I wouldn't really know what to search for.
  10. I don't think the temperature change will be big. While I initially thought that the stored energy was a good way to look at it (and there's a lot to be said for starting any problem with "can I apply the conservation of energy to this question") I'm no so sure any more. Practically speaking, PV is a constant The force on the projectile is its area A (the area of the barrel) times the pressure P. From that you can get an acceleration of the projectile. From that, in turn, you can get a distance traveled (x) in some small time interval The initial volume is V1. The volume after that short time interval is V2 =V1 + Ax With that new volume you can calculate the pressure P2 and start again OK, if you like calculus you can take the limit for a time interval tending to zero and get an exact formula, but I'd just do this by itteration.
  11. Let's face it, if he had white phosphorus he'd probably be dead by now. Come to think of it, burning red P in a sealed tube with sugar might make enough white P to be a problem. You would need to be unlucky but...
  12. There are not many safe (even in relative terms) mixtures containing chlorates and even fewer "safe" mixtures containing red phosphorus. If you know little enough about this to ask the original question you need to do a lot of research before playing with these materials. I have only had occasion to work with red phosphorus once. I wasn't altogether happy working with it. I couldn't turn the job down because it was part of a fatal accident enquiry. I analyse explosives (among other things) for a living. Really, if you have some red P take it outside, put it on something you don't care about and set fire to it before you hurt yourself.
  13. The very first motor, (Mr Faraday's) used DC and a permanent magnet. It also used a pool of mercury as the "sliding" contact so I don't really advise copying it. Here's a comparison. http://www.popsci.com/popsci/how20/252c8c09c166d010vgnvcm1000004eecbccdrcrd.html
  14. "why even bother to post that in here John????" As a joke-OK, I'm a chemist not a comic. BTW, new developments in science often start as contrary opinions- don't be too rough on them.
  15. I think PV = 1/2 MV^2 is the best start but it will not really answer the question. You won't drive a projectile to faster than the speed of sound no matter what pressure and volume you use (unless you do some really complicated things). The speed of sound is roughly the same as the speed as the molecules; if the molecules of the gas are only doing 300 m/s they cannot push a projectile that is moving faster than that because they cannot catch up with it.
  16. The old fashioned approach was to take the sum of the left and right channels which is usually mainly the vocals or the difference between the 2 channels which is largely everything else. Of course this only gives you a mono signal for each and it relies on the idea that the singer is in the middle of the stage.
  17. NH4NO3 can decompose to give N2O and steam, it can also give N2, O2 and steam depending on the conditions- the important fact is that it can do this exothermically so if you get enough of it together it can be made to explode. Adding certain impurities like a fuel or (for some obscure reason) chlorides increases the likelihood of this reaction. The NH4Cl isn't a reactant, but a catalyst. NaNO2 should be pretty dull unless there is some impurity present to act as a fuel.
  18. I don't need a top ten; I just need lots of gold.
  19. Ther are certainly phenolic compounds in a number of drinks. In Whisky (my drink of choice as it happens) the presence of pheolics gives what's called a "peaty" flavour. The off flavour in wine described as "corked" is due to trichloroanisole. (OK, that's not quite a phenol, but it's close.) I think the printed circuit board smell is more like benzoquinone, but it's certainly similar to phenol. Perhaps I should stop sniffing at so many chemicals.
  20. Essentially, its because on one side of the equivalence point it's acid; on the other side it's a base and it has to get suddenly from one to the other.
  21. Ignoring the patronising balderdash in this quote "so where do white people come from, i will tell you but you wont exept it because you have no understanding . i am not here to down you . i am here only to give the truth......... ALBINOS " leaves a question. If white people are descended from albinos how come we white people are not blond haired pink eyed etc? Albino people lack the abillity to synthesise melanin so they are very pale. I accept that a mutation could switch that synthesis back on (the odds are against it but that's another matter). Then you would be back where you started- if you got all the albinos from black families and put them on an island (with a lot of sun-tan oil) after many generations of albinos some of them would revert back to black. What you wouldn't get in a hurry would be white people. You say yourself that albinos in black families don't look like white people then you say that white people are just these same albinos with a bit of black mixed in. That simply doesn't make sense. Allatomear, there's an article in this week's New Scientist about the genetics of skin colour- it's very compicated and they still haven't got it all sorted out yet. These people have been doing the research and I sugest that you read it before making statements like "people have no understanding, i will tell you the truth but thats only if you want to know. first you should learn about genetics and natural selection. your own people hind the truth from you. after you read this, instead of debating get knowledge. read and learn , and then sort out the information ." BTW, the analogy with paint mixing gets used time and again by creationists who don't understand evolution.
  22. I may be missing something here but if I was right about that equation above doesn't the constancy of the speed of light follow from Maxwells equations? And if it does then does that mean that it was Maxwell, rather then Einstein, who first theorised that c is a constant. (OK, that's not how he put it)
  23. Congratulations! You have spotted your teacher's mistake. If you add an acid (and ammonium salts are acids, albeit weak ones) to a mixture of bases like carbonate and hydrogencarbonate, the acid will react with the strongest base first. For what it's worth if you did have carbonate and CO2 present they would react to give hydrogencarbonate Na2CO3 + H2O +CO2 --> 2 NaHCO3 A good way to embarrass the teacher would be to ask why nobody saw the bubbles of CO2 they said had been produced, but I'll let you decide if that's a good idea.
  24. It really depends on the gas. In very cold weather you can work with liquid butane in a class if you want (and I've done it). Similarly in very hot weather (over about 35C) ether boils as soon as you open the bottle. For nitrogen and oxygen (and lots of others) you need to understand critical temperatures and pressures (above the critical temperature the gas will never condense to form a liquid no matter how high the pressure). For nitrogen you need to cool it below -147.1 and compress it to at least 33.5 atmospheres. Not really home experiment territory.
  25. I don't see how a vacuum can, so to speak, "know" that it is moving in order to change its impedance accordingly. If I am running and I hit a tree I will become acutely aware of the relative velocity of the tree and me. How can I measure my speed with respect to a vacuum in order to allow for this when measuring its impedance, permittivity or permeability ?
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