Sciencemadness Discussion Board - low temp burning

low temp burning

invader_gir - 26-6-2005 at 16:55

Hello,

in chemistry class, my teacher told me that she used to put this stuff on her hands and light it on fire. It didnt burn her, and she said that it felt like warm tap water. She no longer does this though, and she wont tell me what was in it. Any thoughts?

neutrino - 26-6-2005 at 17:39

Depending on how her hand was oriented, simple ethanol could have been used. If you really are interested in low temperature flames, look up carbon disulfide (CS<sub>2</sub>

. It burns with a relatively low temperature (I don't have the exact numbers at hand), and has an autoignition temperature of ~90*C. Just be careful, as CS<sub>2</sub> is not too healthy. (MSDS)

sparkgap - 26-6-2005 at 17:50

I am sure your teacher DID NOT use napalm.

neutrino: I wouldn't pour carbon disulfide on my hand and ignite it for no good reason if I was at least a half-decent chemistry teacher, 'no?

sparky (~_~)

P.S. Ethanol or isopropanol, I suppose. Some tricksters where I live use strongly fermented sugar cane juice for this demo.

[Edited on 27-6-2005 by sparkgap]

neutrino - 26-6-2005 at 18:49

There was a time when they didn't know it was so dangerous. Demonstrating the cool flame of carbon disulfide was popular back then.

BromicAcid - 26-6-2005 at 19:00

Actually I remember reading that the popular mix was a concoction of carbon disulfide with carbon tetrachloride. I think there are some good conversations that can be found in google groups on cold burning compositions.

Edit: 6 of the 10 topics on the first page of search results for (Carbon tetrachloride disulfide) in google groups are on cool burning flames.

[Edited on 6/27/2005 by BromicAcid]

chemoleo - 27-6-2005 at 08:34

Well, if it's stuff without definition, it also could be nitrocellulose - it burns so fast it won't harm, althoguh that doesn't equate with cold burning temperatures.

[Edited on 27-6-2005 by chemoleo]

runlabrun - 27-6-2005 at 16:48

I do this one in class myself!! (of course while the head teacher isnt watching... ive already gotten into trouble for it several times!)

Its just methanol... get ~100mL and pour it all over your hand and wave it swiftly through a lit bunsen on the yellow flame. It burns and evaporates quick enough and you dont even feel a thing. To avoid any singes or burns you just need to keep your hand moving, it increases the evap rate.

This doesnt last too long so unless your teacher sat there for an extended period of time on fire i would say he or she is doing the same as what i do.

-rlr

12AX7 - 27-6-2005 at 17:24

There's also a firegel product used by the stunt industry that's an insulating, cooling (fireproofing) gel. You can pour gasoline over it and burn for a half a minute before you get warm.

Tim

sparkgap - 27-6-2005 at 21:09

"...it also could be nitrocellulose - it burns so fast it won't harm..."

Those words of yours remind me about the time clothes were made from nitrocellulose. One unfortunate young lady who wore her frilly gown to a social function and went a bit too near the candle saw all her clothes go up in a puff of smoke, to her consternation and the surprise (or was it delight

) of her male companions. Thus it was that nitrocellulose was stigmatized as "mother-in-law's silk".

Tim, would you happen to know offhand what was the brand of said fire gel?

sparky (^_^)

12AX7 - 27-6-2005 at 21:13

Don't know, I just know it's used by stuntmen. If you happen to be in California I'm sure it's not hard to get.

Tim

JohnWW - 29-6-2005 at 01:34

White phosphorus exposed to air glows in the dark due to slow combustion - but it is poisonous.

gm137 - 29-4-2007 at 05:47

I do the "flaming hands" demonstration for my classes frequently: I just use Acetone, which burns impressively but absorbs so much heat as it evaporates that your hands stay cool. Having said that, impurities or just plain bad luck can lead to some nasty burns, which sort of takes the kick out of the trick.

I am a fish - 30-4-2007 at 02:39

Make sure that you use a hairless region of skin. Hairs will act as little wicks, and will greatly increase the combustion rate.

(Richard Feynman describes this in his memoirs. He did the experiment as a child without any problems, but when he repeated it as an adult, he burnt himself.)

Quote:

Originally posted by JohnWW
White phosphorus exposed to air glows in the dark due to slow combustion - but it is poisonous.

And it is also likely to spontaneously set alight, in which case you will end up with third or fourth degree burns.

garage chemist - 30-4-2007 at 03:58

A 50/50 mixture of ethanol and water can be used too, this mixture is also used to demonstrate its cool burning by soaking a paper handkerchief in it and igniting, the paper is not scorched but the mixture burns with a large flame.

DrP - 30-4-2007 at 05:37

Quote:

Originally posted by garage chemist
A 50/50 mixture of ethanol and water can be used too, this mixture is also used to demonstrate its cool burning by soaking a paper handkerchief in it and igniting, the paper is not scorched but the mixture burns with a large flame.

I have read this before - I think that woelen mentioned it somewhere. We used to do it at school with lighter fuel - but I never really thought it was very sensible.

EtOH/H20 50/50 sounds alot safer.

JohnWW - 30-4-2007 at 07:56

There are some bourbon whiskies and Russian vodkas and naval rums ("100 proof") sold that are 50% ethanol, although they are produced in much smaller quantities and at significantly higher prices than the regular strengths, which are between 37 and 40% and sometimes 43%. Absinthe is much stronger, usually between 60 and 85% alcohol, although it is mixed or diluted before drinking.

I am a fish - 30-4-2007 at 13:18

Quote:

The effect could probably be improved by dissolving sodium chloride in the mixture. Ethanol burns with an unimpressive pale blue flame. Adding sodium will impart a strong orange colour, making the flames look more impressive.