Sciencemadness Discussion Board

A Road Flare?

elementcollector1 - 21-5-2013 at 07:54

Over the weekend, as I was at a Boy Scout camp, a very odd thing happened. A guy walked up to me and said 'you're the chemist, right?' as I was sitting by the firepit. I nodded, and he gave me a roadflare with the end cut off. Taking out the cut-off end, he tossed it into the fire, and soon enough it burned with a brilliant red flame. I assume this is strontium nitrate?

Now, as I understand, the components of a flare are a nitrate salt with a corresponding color, sulfur, and carbon (essentially gunpowder?).
To separate these, I would first boil the crushed-up road flare mix in water to separate the strontium nitrate, then boil it in some solvent that sulfur is soluble in (hard to get toluene and impossible to get hexanol where I live, alternatives) to separate the pure sulfur, and then I should be left with just carbon, correct?

bbartlog - 21-5-2013 at 08:09

Composition varies: http://www.spiegl.org/rocket/flare/flare.html

Sulfur is slightly soluble in acetone. Anyway, rather than try to separate the flare cleanly into its separate constituent chemicals (as you imply), which is really fairly difficult, I think you should just aim to extract one.

ScienceSquirrel - 21-5-2013 at 08:20

You would be better off boiling the flare with water to extract the strontium nitrate and then subliming / melting out the sulphur rather than using a solvent.
This is how sulphur was purified in antiquity and still is where it is mined on an artisan scale around volcanoes.

http://en.wikipedia.org/wiki/Sulfur#Production

elementcollector1 - 21-5-2013 at 08:45

With a MP of 113 C, melting it out is tempting - but how do I separate the carbon? By density? Carbon shouldn't be soluble in molten sulfur...
As for sublimation, it boils at 444 C - not exactly what I can do with a hotplate. A blowtorch, maybe, but that leaves me to worry about oxidation, even if I just heat the metal crucible containing the sulfur from the outside.

blogfast25 - 21-5-2013 at 09:51

Quote: Originally posted by elementcollector1  
With a MP of 113 C, melting it out is tempting - but how do I separate the carbon? By density? Carbon shouldn't be soluble in molten sulfur...
As for sublimation, it boils at 444 C - not exactly what I can do with a hotplate. A blowtorch, maybe, but that leaves me to worry about oxidation, even if I just heat the metal crucible containing the sulfur from the outside.


Not sure what you mean here: of the flare composition only the Sr nitrate is water soluble, so simple extraction by hot water leaching and work up by recrystallization should be quite straightforward. Seems an expensive way of obtaining Sr nitrate though: you're paying for all the profit margins made by producing the flare! Sr nitrate maybe a bit UTC in some areas but it's not that hard to get.

chemcam - 21-5-2013 at 10:02

I did this extraction like a month or two ago and I got about 121 grams of strontium nitrate/KClO4 from a 15-minute ORION flare. If it is that type being used there is Sulfur, Sawdust, Strontium nitrate and potassium perchlorate. It is very easy to do, dissolve everything in water, filter out insoluables, evap. water. The Sr(NO3)2 and KClO4 will be difficult to separate. Flares only cost $1.00 where I live so it's not bad way.

Extraction: Sr(NO3)2+KClO4 from Emergency Flare
This video is done by me but I left a lot of it out because at first I wasn't going to film it. It is an easy process.

blogfast25 - 21-5-2013 at 10:30

Quote: Originally posted by chemcam  
The Sr(NO3)2 and KClO4 will be difficult to separate. Flares only cost $1.00 where I live so it's not bad way.



KClO4 is almost insoluble at 0 C (0.76 g/100 ml, acc. Wiki). Should be a doddle, really.

chemcam - 21-5-2013 at 11:17

Great, so the entire process is very simple, no need to melt anything or use expensive reagents. Water does the trick, what a magic combination of elements.

Bot0nist - 21-5-2013 at 11:23

They used to be a decent source of red phosphorous as well. Many of them would have a nice sized blob of it on the top... I imaging the damn cooks have spoiled that for us now, as well.

[Edited on 21-5-2013 by Bot0nist]