John Cuthber
Resident Experts-
Posts
18385 -
Joined
-
Last visited
-
Days Won
51
Content Type
Profiles
Forums
Events
Everything posted by John Cuthber
-
"The conc acid will remove water quicker than normal desiccants" When the water leaves the solution, how does it know to hurry up because there's some sulphuric acid out there?
-
I suspect that there are a very large number of possible answers to the question. For example, you could put the two items down and go off and do some vital research that gets you a Nobel prize. Or you could put them down and vegetate in front of the tv. or, well lots of things really.
-
Chemistry of carbonates & bicarbonates - new article
John Cuthber replied to adianadiadi's topic in Science Education
Odd variety of granite that reacts with acids like that. -
Baking powder?
-
You can remove some of the water under vacuum, but the stuff will tend to decompose.
-
Good point, but it works both ways; if the current flows for a short enough time then it won't have any effect.
-
I suspect it's a matter of Joules that can kill, rather than Watts.
-
Yes.
-
Bacteria and radio waves?
John Cuthber replied to Green Xenon's topic in Microbiology and Immunology
I mean that every living thing emits electromagnetic waves of all wavelengths. So do the non living things. -
Yes, but the effect would be so slight that I wouldn't want to have to measure it.
-
Yes, you can do it badly. The first holograms were made without lasers. Strictly, this wiki page http://en.wikipedia.org/wiki/Dennis_Gabor about the inventor is wrong. You can't make holograms without coherent light.
-
400 nm laser that emits 1-photon-per-second -- possible?
John Cuthber replied to Green Xenon's topic in Physics
There would be a vast number of photons bouncing about coherently inside the laser. Almost all lasers act this way; most photons don't get out. -
Bacteria and radio waves?
John Cuthber replied to Green Xenon's topic in Microbiology and Immunology
Every living thing is at a temperature above absolute zero and therefore emits em radiation at all wavelengths. OK the emision rate of visible light from something growing in my fridge is pretty near zero but I can calculate the rate if I get bored enough. If you stick your biology in an NMR machine you can get a whole lot more interesting RF radiation from it. -
400 nm laser that emits 1-photon-per-second -- possible?
John Cuthber replied to Green Xenon's topic in Physics
I can't imagine why you would bother but... Imagine you have a normal dye laser that emits somewhere near 400nm and you tune it with a grating or whatever to exactly 400nm (as near as you want). This laser will have an output mirror that reflects very nearly all the photons that hit it back into the cavity in order to maintain the oscillation. Imagine that you coat a bit more silver onto that mirror so it reflects slightly more- the system will still work as a laser. You might have to drop the input power to keep things balanced but that's not difficult. Keep raising the reflectance of the output mirror and you will get to a point where, on average, you get one photon a second from it. Pointless, but possible. -
It's true that perchlorate is more stable. That's why you shouldn't use it. Because it's more stable it doesn't do anything unless you get it so hot that, once the reaction starts, it's even more violent. Also, of course, it has more oxygen in it. It also has a much higher melting point too so, if things go wrong, it's hotter. Generally anyone who closes their post with "Please take me seriously!! I konw what Im talking about." should raise a flag about their ability, even more so if they can't spell sulphur. There is, with this experiment, a small risk. If the chlorate is contaminated with some reducing material then the reaction may well become violent, even before adding the sweets. You can check this by heating a small amount of the chlorate behind a blast screen before you start. Of course, if it's the same batch as you used last time and it was OK then, you should be able to use it again (provided, of course, that you can be sure that it hasn't been contaminated in the mean time).
-
No nuclear, no petrol; no hope.
-
Presumably there's another 1% bad maths.
-
Generally on ebay.
-
Adjusting the pH of a buffer solution
John Cuthber replied to Ezio's topic in Biochemistry and Molecular Biology
It will work, and it's quite comon practice. Ideally you might choose to use the same acid and base that the buffer is made from (e.g. for an ammonium citrate buffer you would use ammonia or citric acid). Also, ideally, you use a solution of the acid or bas that's the same molarity as the buffer but, most of the time, a bit of whatever acid or base you have handy will do. It would make most difference if you needed to add a lot, in which case you haven't made a good choice of buffer in the firt place. -
My guess is that someon who is asking that question wouldn't know a Gibbs free energy if it bit them However, it's worth noting that in the examples given the valencies of the elements don't make sense. H2Cl, for example, doesn't exist because it would need a very odd valency for the chlorine. A table of valencies is, imho, probably a lot more use to Lawlord than a discussion of thermodynamics.
-
Is There a Double Standard When Democrats Ridicule Minorities?
John Cuthber replied to Pangloss's topic in Politics
Imagine that the same person made both coments. Would you consider them equally offensive? I would certaily be more bothered by someone saying, in effect, that he was proud to be racist than by someone making one dumb comment then apologising for it. As I see it one person has been forced to resign while the other hasn't, simply because the remarks he made were less acceptable. -
I think that someone calling themself "truedeity" and posting a thread called "Dream Frequency Reality Singulairty " is a pretty strong hint that it's not something I'm going to be interested in. When I saw that the post consisted of two words and a link, it made me even more certain.
-
I think I liked it better when he just posted a link.
-
It would, if anyone cared, be perfectly simple to check on whether it produces a back emf. Don't connect it to a battery, just hook it up to a voltmeter (that osciloscope would do nicely) and then trun it by hand. If you get anything on the 'scope then it's a back emf and the claims are false. Anybody care to run a sweepstake on how long it takes Steorn to run this test? Can I bid on "never"?
-
Ice is generally transparent, colourless, smooth, cold to the touch, and slippery when it's wet; so it's nothing like glass at all. Anyone who has ever dropped a glass while washing it or because its surface was wet will know that wet glass is quite slippery. Aparently newspaper editors in the UK can cope with this and so can the readers.