Could a small crystal of mercury fulminate really do so much damage? Mercury Fulminate (or fulminate of mercury, as Walt rightly calls it) Hg(ONC)2 is a very unstable and explosive compound. Although first prepared back in 1800, because of its instability the crystal structure was only fully determined as recently as 2007. It is prepared by reacting mercury with nitric acid and then adding ethanol . The crystals are usually brown to grey (due to colloidal mercury) and large crystals are extremely unstable. Silver fulminate can also be prepared in a similar way but is too sensitive for commercial use, though some crackers and children's toy caps (e.g. Fun Snaps etc.) sometimes make use of it.
Pressure changes, vibrations and shock can lead to detonation. The explosive properties can be demonstrated in the lab by hitting a very small crystal (ca. < 1mm3) with a hammer
(Take the same precautions as you would when demonstrating Nitrogen triiodide explosive crystals ). Detonation produces mercury vapour, carbon monoxide and nitrogen.
One explosion pathway could be:
Hg(ONC)2 → Hg + 2CO + N2
Walt's crystals are transparent and 1000 times larger than the demonstration crystals mentioned above. If they could have been prepared at all without detonation they would have been very unstable to carry around but could indeed have created a very powerful explosion. Further, the shock wave would no doubt have detonated the other crystals in the bag on Tucos desk. I doubt there would have been such a great quantity of flames issuing from the explosion as you see in the film. Walt and Tuco had survived the explosion they would not have been able to hear for a long while!
References and notes
 Breaking Bad, episode 6 of the first series DVD, Sony Pictures, 2008.
 See the handling precautions for Nitrogen triiodide, EiC, Exhibition Chemistry, May 2010.
 Explosives, Chapter 11, John Reid, Pelican Books (worth finding on Abebooks etc.)
How teachers can use these articles in a lesson
Why Hollywood Science
Open University Hollywood Science web site
Call for clips - do you have a film clip that needs investigating?
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