John Cuthber

Resident Experts
  • Content Count

    16441
  • Joined

  • Last visited

  • Days Won

    19

Everything posted by John Cuthber

  1. Is this "Transfusion blood is heated in water, not a microwave oven. Why? Because if heated in a microwave, the blood becomes toxic and more than one patient has died as a result." backed up by any peer reviewed data? If someone died was it due to tocicity or to local overheating causing clotting? Is this just an urban myth?
  2. Actually photons have mass. It's given by E=MC^2 and E=hf. (Energy, mass, speed of light, Planck's constant and frequency) They are atracted by gravitational fields (The effect is usually refered to as "gravitational lensing"). They also carry momentum and exert radiation pressure. There is a cop out on the "nothing can travel at the speed of light" What is forbidden is accelerating anything with a rest mass (ie a mass, even when it's stationary) to the speed of light. Photos have zero rest mass (a slightly meaningless idea since a photon at rest doesn't exist). The fact that we cannot produce a perfect vacuum does not stop us being able to establish the speed of light in a vacuum. That sounds like a paradox, but it isn't. We can measure the speed of light in air at one atmosphere pressure, we can do the same at half an atmosphere, a tenth, a thousandth and so on. Then we can plot a graph of speed vs pressure and draw a straight line through the points. We can carry that line on until it hits the axis for "pressure = zero" and read the value of the speed in a vacuum from that. I hope this answers your question.
  3. ecoli, What aldehyde and what triple bond? The classic method for the first part, IIRC, is reduction by magnesium. Look for stuff about pinacol. I'm not sure abouty the second; perhaps dehydration to the epoxide then reduction?
  4. Try this page (In general, try using a search engine) http://polymer.matscieng.sunysb.edu/OH_handouts/polyFoam.doc.
  5. I think this http://www.mutr.co.uk/prodDetail.aspx?prodID=1194 thing about memory alloys is about as close as you will get.
  6. Quite a lot of chemicals are worth taking the trouble not to get on the skin too. Of course, provided that you don't come into contact with the Br2 it's also safe for experimenting. All chemicals are safe as long as they aren't anywhere near you. (Explosive and radioactive ones can get you at a distance.) Fundamentally, (and this is an important point) there are no dangerous chemicals. There are lots of dangerous things to do with chemicals and for some chemicals there's a bigger choice of dangerous things to do than others, but the danger is a matter of what you chose to do with them- not a property of the chemical itself. A beaker of NH4Br isn't a bigger problem than a beaker of NH4Cl. On the other hand, if I wanted to make some smoke I'd use the chloride unless I had a really good reason to risk the neurotxicity of the bromide (and possibly the carcinogenic bromate too)
  7. I don't think there's enough information to answer the question. As it happens the formula of hydrogen selenide is H2Se This decompses to give H2 and Se. The Se then reacts with the tin I think it will give SnSe- it might be SnSe2 but it doesn't matter because it takes up vrey little space whichever compound is formed. H2Se --> H2 + Se The H2Se and H2 have the same volume because there are the same number of moles of each. However, imagine that you chose H2Se2, the selenium equivalent of hydrogen peroxide. It too will decompose to give H2 and Se (which will be removed by the tin) H2Se2 ---> H2 + 2Se There are still the same number of moles of gas on each side of the equation so the pressure won't change. I'm not sure how stable H2Se2 is- it might not exist (though a web search for hydrogen diselenide does give some results so I think it's real) The point is that it (H2Se2) would give the same result as H2Se. You cannot distinguish the 2 possible formulae by that experiment.
  8. A couple of thoughts. 1 A plane flying in the right direction (heading into the sunrise I think) on the equator is, in effect, on a conveyor belt travelling at about 1000MPH (this conveyor is normally called the earth). This wouldn't make any real difference to its abillity to take off because the air is being dragged along by the earth. Any conveyor that could run under a plane that was trying to take off would drag an enormous amount of air with it. This would create at least some lift. Once the plane starts to rise the friction is reduced. If you raise the belt speed in order to try to compensate for the reduced frictional drag then you will incerase the amount of air dragged over the wings and create more lift. I think that the plane takes off but I wouldn't like to pay for the conveyor or the fuel to run it. 2 Anyone got a vertical take-off plane?
  9. In terms of the LD50 and such the bromides are roughly as toxic as the chlorides but, since bromides are used as drugs acting on the central nervous system, I would sugest steering clear of them.
  10. Since all bromides are toxic I really wouldn't recommend tasting them or inhaling the smoke.
  11. The problem is that, unlike a V de G, it doesn't help you at all. You might as well use a bit of wire connected to the power supply. With a V de G you spray charge onto a belt and the motor drags that charge towards the top sphere- in doing so it has to overcome the electrostatic repulsion between the charges on the belt and that of the top sphere. This means that work is done on the charges and their potential is raised. The current is the same as that sprayed onto the belt by the HT power suuply, but the output voltage is much higher. With an electron beam this doesn't happen so the output voltage is the same as the input.
  12. That mixture of hydrocarbons is fairly good at extracting things from water so, unless you happen to have something very water soluble in it as an impurity, washing with water won't remove the impurity. If on the other hand the stuff is very water soluble then it's unlikely to disolve in the naptha in the first place. Having said that, it looks like you have found a source of pet ether which was the original problem.
  13. Can anyone else see why this "Shellite from the hardware store is generally an ok substitute for backyard extractions" is exactly why this "if you dont trust it's purity wash it with distilled water before use (ie add water, shake, let separate into layers - the shellite floats ... discard water layer from the bottom)" may not work very well.
  14. Yes, if you are eating "the pill". Otherwise the body's feedback mechanisms make sure that the effects are tiny, certainly less than the natural variation in hormone levels from one person to the next. Anyway, the idea that eostrogens make you gay is utter balderdash. Don't forget that all of us, while in utero, were exposed to female hormone levels nearly as high as our pregnant mothers. If that exposure led to homosexuallity then there simply wouldn't be any straight men.
  15. Last time I was doing this I precipitated the silver with sodium acetate and washed off the copper acetate (you lose Ag this way but you can always recover it as chloride). If you want to get the silver then you can heat the acetate carefully so it decomposes. Since the acetate is slightly soluble you should be able to convert it to Ag2O with excess NaOH, wash it then redissolve it in HNO3.
  16. Don't forget that if it looks too good to be true it probably is. IIRC pyruvate is naturally present in the body, created and used up rapidly so adding a little wouldn't have much effect.
  17. Fractals, like those generated using imaginary numbers, are used for data compression which is reasonably important in this www world. I don't know if the particular fractals they use are calculated using imaginary numbers. "I just fail to see how this makes the equation any more solvable. You still can't have the square root of a negative and just because you put an i down doesn't change this." That's a fair point but I think there are 2 answers. Firstly the mathematicians are happy because now they can write down an answer. If they had to keep on making up "strange" numbers in order to answer lots of equations I think they would have given up, but just one weird number i, seems to do the job. The other reason is that ignoring the fact that i doesn't exist and finishing the calculation seems to work in quite a lot of physics. If it makes the equations work, perhaps it must be (in some sense) real.
  18. John Cuthber

    Brain teaser

    Because we have to shed the waste heat that metabolism generates. We can do that by sweating (the heat is used to evaporate the water) but it's easier to do it if we can lose heat simply by conduction to the outside air. Normally the skin is a fair bit cooler than 37C so the excess heat is conducted (as well as carried by the blood) to the skin. When the air temperature is as warm as 37C we have more difficulty losing the waste heat we generate.
  19. Or, if you prefer a geometric equivalent, the 2 halves of the expression on the right are 2 triangles, put together with a line of n "stars" they form a square. * *** ** ** *** * **** Can someone who understood that and who has a better graphics package than me draw that please?
  20. "the basics behind why planes fly." The classic explanation of how planes fly must logically be wrong. Stunt planes can be flown indefinitely upside down. As for "PLEASE COMMENT" how about, this post is in the wrong place and please don't WRITE IN CAPITALS. As insane alien said a pipe with a fast flowing liquid stream will tend to colapse but the effect is usually small.
  21. The idea of using beta emitters directly as a source of electricity does work. The currents involved are tiny but the voltage can be huge. As for pointing an electron beam at an isolated metal sphere it sort of works but, once the sphere has the same voltage as the accelerator potential of the electron gun the electrons are repelled but the negative charge and the no more current flows onto the sphere. You would do just as well to connect a wire from the high voltage source to the sphere directly.
  22. The reactants get turned into products so, at any given time the rate of change of ammount of reactant with time is negative. Imagine we start with a gram of reactant and that after 5 minutes there is half a gram left. The change in amount of reactant is minus half a gram and the change in time is 5 minutes so the rate of change is -0.5/5 ie -0.1g/min Since we prefer our constants to be positive we chose to use the expression dx/dt=-k[A] (with a minus sign in it.) It's a matter of convention; we could use rate negative constants but they would look odd.
  23. It's not exactly a well kept secret what goes into the tablets. Ingredients Active Ingredients: Each Tablet Contains: Aspirin (325 mg), Citric Acid (1000 mg), Heat Treated Sodium Bicarbonate (1916 mg). Alka-Selzer in Water Contains Principally the Antacid Sodium Citrate and the Analgesic Sodium Acetylsalicylate. Inactive Ingredients: None. BTW, the equation in the first post doesn't reflect what is going on here; in fact that reaction goes the other way.
  24. Sulphonic acids give sulphonamides, phosphoric acids give phosphoramides carbamides are another variation on the theme too.
  25. "in fact I would go so far as to say that NON of the metal elements have a smell exactly (nor their oxides), " YT2095, you might wish to look up the origin of the name "osmium" though I grant that it's unusual.