John Cuthber

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.

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?

"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.

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.

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.

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.

Sulphonic acids give sulphonamides, phosphoric acids give phosphoramides carbamides are another variation on the theme too.

"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.

Nitric acid reacts with HCl which pretty much rules it out.

Often the scheme is to add an acid to a salt then distill out the acid. There needs to be a reason why the reaction goes in the right direction ie the way you want. With sulphuric acid (boils about 300C) you can remove the acid you want eg HCl, acetic, nitric by distilling it. If you were to mix HCl with sodium acetate you would certainly get acetic acid produced. However if you were to try to distill out the acetic acid at least some of the (volatile) HCl would also come over. With H2SO4 that's not going to happen.

H2SO4 is also cheap (industrially, rather than from the shop up the road) and a strong acid.

Phosphoric acid might work for some of these reactions too- it's available and cheap. It's not as strong an acid but that doesn't matter so much if you can remove the product by distillation.

Unfortunately hot H3PO4 kills glassware.

There are about a trillion hits on Google for "amino acid analysis" HPLC. Most of them involve reacting the amino acids with something to make them easier to detect and less polar.

This one seems pretty typical.

http://www.canr.msu.edu/comparativenutrition/Amino%20Acid%20analysis%20of%20Hydrolysates.doc

I can't say I've tried it but it looks like a good place to start.

Of course, that's OK for a UV or fluorescence detector. LC/MS can be a bit fussy. You will need a volatile buffer rather than sodium acetate and you might need some clean-up stage.

I know you are not going to leach a lot of Be out of emeralds but it's nasty stuff so be careful.

BTW, congratulations on finding the commonest of the transition elements.

"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.

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.

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.

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.

Why do you want to put gelatine down an HPLC?

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.

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?

The nerve gases are orgoanophophates.

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

"closest thing i've found is the italian trade organization"

Close but this is the sort of stuff I meant.

"http://www.ocioptics.com/ito.html"

"I don't want to be a spelling nazi"

Then don't.

I think the lemon juice might be as irritating as the Epsom salt.

Anyway, I can't see this working.

I know how hot you can run glass. I wondered about the ITO.

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?

Does anyone know what the upper temperature limit for ITO on glass is?