from the ph'nglui-mglw'nafh-Cthulhu-R'lyeh-wgah'nagl-fhtagn dept.
IFL Science has an article on Burning NH4Cr2O7 With HgSCN (ammonium dichromate and mercury (II) thiocyanate, respectively).
This is the reaction that produces a "crawling tentacles in a fire pit" effect, seen on a number of animated gifs and youtube videos, described in TFA as "tentacles are crawling out of a portal to Hell".
What appears to be tentacles is actually what happens when heat is introduced to mercury (II) thiocyanate. The white solid expands when it's heated to become a dark, tentacle-like mass due to its decomposition to carbon nitride. In addition, sulfur dioxide and mercury (II) sulfide are also produced. The reaction is appropriately nicknamed the "Pharoah's Serpent" and was sold in stores as fireworks until people realized it's toxic.
The article contains a Youtube video link, and also IFL Science has an earlier article on burning HgSCN (Mercury thiocyanate), which by itself is a creepy chemical reaction. There's also a 10 minute Youtube video available on how to make the Pharaoh's Serpent, with more detail on the reactions involved.
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Mentalfloss has a collection of chemical reaction videos, with explanations of the processes involved.
Each minute, a whopping 100 hours worth of videos are uploaded to YouTube—and a small, yet endlessly fascinating number of those are chemical reaction videos. To explain what exactly is happening in some of these videos we reached out to an expert at the American Chemical Society, John M. Malin, Ph.D, to let us in on some of these awesome chemistry secrets.
This has some overlap with the content from the previous story on burning NH4Cr2O7 With HgSCN, together with a bunch of additional experiments.
(Score: 3, Interesting) by bziman on Tuesday November 11 2014, @07:58PM
How did they ever discover this... and... why?!
Seriously, though, I'd love to know what compelling someone to find these compounds, mix them, and set them ablaze. Where they just trying stuff at random? Do each of these compounds do something useful, and mixing them was expected to do something useful?
If they were going for a "cool" reaction, how did they come up with the hypothesis?
Or was it just a typical group of drunk college students pilfering from the lab and setting stuff on fire, and getting lucky?
(Score: 3, Interesting) by Blackmoore on Tuesday November 11 2014, @08:12PM
people actually get paid to do this sometimes.
http://pipeline.corante.com/archives/things_i_wont_work_with/ [corante.com]
http://en.wikipedia.org/wiki/Dioxygen_difluoride [wikipedia.org]
D. Lowe. "Things I Won't Work With: Dioxygen Difluoride"
http://pipeline.corante.com/archives/2010/02/23/things_i_wont_work_with_dioxygen_difluoride.php [corante.com]
http://en.wikipedia.org/wiki/Chalcogen [wikipedia.org]
Lowe, D. (May 15, 2012). "Things I Won't Work With: Selenophenol". In the Pipeline. Retrieved November 25, 2013.
http://pipeline.corante.com/archives/2012/05/15/things_i_wont_work_with_selenophenol.php [corante.com]
(Score: 3, Informative) by VLM on Tuesday November 11 2014, @08:35PM
If they were going for a "cool" reaction, how did they come up with the hypothesis?
Note, I dropped out of chem after about two years and if you think you can get health and safety advice from HN you must be insane.
First, the thiocyanate all by itself will burn or do the snake thing when heated, the mercury compound is merely being used as an oxidizer to help it burn.
Why screw around with this to begin with? Assuming you've got a hankerin for carbon nitride compounds (why, is a whole nother story) starting reagents involving some kind of cyanate isn't too utterly ridiculous. And chromates/dichromates are super strong oxidizers so it seems a "reasonable" idea to light it up. A thiocyanate is a cyanide with sulfur and this mercury one is not terribly soluble in water (although soluble enough to kill you if you eat it, apparently), so you won't have much water contamination (which would lead to CO or CO2 in the output) And nothing goes together like mercury and sulfur so they'll be out of the final product, mostly. And ammonia is a pretty boring gas that'll get out of the way. So I can see someone Fing around with this mix thinking he'll get some fascinating carbon nitride compounds, and instead ending up with a huge messy pile of "snake".
So think about the parts. You got a thiocyanate thats barely stable looking and when it "fractures" the mercury and sulfur will be stable and outta the way. The dichromate is a strong oxidizer to "kick it off" hopefully not explosively. The ammonia will just go away. It seems a fairly reasonable experimental plan. Mercury is dangerous but the thiocyanate isn't terribly soluble, nothing like the organometallics that'll kill you and the end product is boring cinnabar ore, pretty much. Personally I'd worry the most about the chromate ions floating around all bored and looking for a liver or lungs to eat, but whatever. Things were different back then.
Note that unless you're about 150 years old, the "snakes" you played with as a kid are a plastic-ish substance.
(Score: 3, Informative) by VLM on Tuesday November 11 2014, @08:36PM
the mercury compound is merely being used as an oxidizer
damn editing
the chromate compound is merely being used as an oxidizer
(Score: 2) by Dunbal on Tuesday November 11 2014, @10:40PM
" not terribly soluble in water (although soluble enough to kill you if you eat it, apparently)"
People just keep forgetting that you don't have water in your stomach. You have 0.1 M HCl. This is something the "colloidal silver" crowd never get, and it explains why perfectly insoluble "colloidal" metallic silver end up producing Argyria, because while silver is not soluble, silver chloride is VERY soluble.
(Score: 2) by VLM on Wednesday November 12 2014, @12:24PM
Ouch, good point, the first line of my post is very relevant to your comments.
(Score: 2) by wonkey_monkey on Tuesday November 11 2014, @09:35PM
Where they just trying stuff at random?
Science!
systemd is Roko's Basilisk
(Score: 2) by wonkey_monkey on Tuesday November 11 2014, @09:22PM
The article contains a really blurry lo-res Youtube video
The multiple tentacles are a bit creepier to watch, but this one here is HD with an informative commentary:
https://www.youtube.com/watch?v=PC3o2KgQstA [youtube.com]
systemd is Roko's Basilisk
(Score: 0) by Anonymous Coward on Tuesday November 11 2014, @11:10PM
Pretty sure this reaction is noted in many old-school pyrotechnic texts.
Soluble or not, anything involving chromium and mercury is a hazard to work with. Heck, table sugar and conc. H2SO4 makes for a heck of a "snake" demo and are probably both less hazardous imho.
(Score: 1) by Ian Johnson on Tuesday November 11 2014, @11:25PM
The video would have been far better if he'd filmed the reaction at a fixed zoom level. Instead he zooms in, causing the video to go out of focus, then he zooms out, then in, then out. You end up watching is antics with the zoom instead of paying attention to the video content. By the end of the video I didn't know nor care what it was about.
Just because a feature is there doesn't mean you should use it!