Mercury fulminate is an unstable primary explosive compound. Mercury fulminate was discovered in 1799 by the British chemist Howard. It was introduced by the British gentleman Wright in 1821 as an effective filler for percussion caps. Alfred Nobel got its patent in 1867 for blasting caps, and was the single most used compound for that application until very recently. It is not used today for that purpose because of more stable explosives from modern chemistry taking its place, but its high power, ease of manufacture, and relative stability (as compared with some other improvised primer choices) makes it an attractive choice for improvised blasting caps even nowadays. Below, FOR INFORMATIONAL PURPOSES ONLY, the manufacture of a small batch is outlined. The entire synthesis takes about 2 hours. Do not try to scale up the procedure, as thermal runaway or excessive crystal stress may result in a detonation.
Once again I discourage anyone to attempt these procedures, and if you choose to do so you are doing it at your own risk.
1,1g Mercury metal (Hg(l)) (d. 13.543g/cc)
50mL glass beaker and 100mL flat bottom glass balloon.
10mL 68% Concentrated Nitric Acid (HNO3(aq)) (d. 1.41g/cc)
15mL 99.8% absolute ethanol ((C2H6O)(l))
Distilled Water, Ethanol (l)
The reaction goes as follows: 1st step involves the nitration of mercury metal with excess nitric acid:
Hg + 3 OHNO2 => HgNO3 + OHNO2 + NO2
Secondly, the mercury nitrate and excess acid are added to ethanol, forming the fulminate:
HgNO3 + HNO3 + C2H6O => Hg(ONC)2
Here all the materials and reactants used for the synthesis of mercury fulminate can be seen: From the back row to the front, from left to right:
100gram bottle of Mercury metal, 100mL bottle of 65% Conc. HNO3, 1L of Distilled Water, 1L absolute ethanol.
Glassware is one 50mL glass beaker, one 100mL flat bottom glass balloon, both Pyrex. On the glass beaker is the stirring rod. The Pipette is between the two large plastic bottles. To the extreme right a 400mL beaker with filter paper is seen: This will be used to carry out the filtrations.
For this procedure 10mL of 65% analytical grade nitric acid were measured out and pipetted into a 50mL beaker, onto which 1.1g of mercury were pipetted and added. A vigorous reaction ensued, during which large amounts of Nitrogen Dioxide (NO2) gas were released and some heat is produced. The reddish/Brown gas is highly toxic as well as being a very powerful oxidizer, and all contact should be avoided. This step should be conducted under a fume hood. If the reaction between the acid and the mercury does not start immediately, the solution should be heated gently (to no more than 70C).
Once the reaction was complete a greenish liquid (mercury nitrate solution) formed in the bottom of the beaker. This was left to stand for a few minutes until it has returned to room temperature and most of the nitrogen dioxide gas had escaped.
15mL of absolute ethanol were than pipetted onto the 100mL flat bottom glass balloon, and it was warmed gently. The now cold mercury nitrate / nitric acid solution was added to the warm ethanol, and within a few minutes a vigorous reaction ensued, and the external heating was stopped (the reaction produces a great deal of heat and is self sustaining).
This second reaction lasts approximately 10 minutes, during which time the solution bubbled vigorously and produced dense white fumes (both poisonous and flammable. Again this step should be performed in a fume hood). As the reaction neared completion, the amount of gas and bubbles produced decreased and crystals were seen precipitating at the bottom.
Once the reaction was complete a small layer of crystals had formed at the bottom. These were the explosive fulminate, which now had to have all traces of acid removed from it in order to become stable.
The crystals were removed from the solution by filtering, and while at the filter they were washed with an extra 15mL ethanol, 50ml distilled water and than finally 15mL ethanol. This ensured that all traces of acid were removed, and also reduced the drying time (since ethanol is more volatile than the distilled water).
Once dried, the crystals formed a grayish/yellow mass that was both poisonous and sensitive to static electricity, friction and impact. The uttermost care should be taken to ensure that these are not bumped, scraped or handled roughly.
Despite the use of analytical grade reactants throughout the procedure, the crystals still contained some small amount of impurities, evidenced by their tint.
This is acceptable for commercial applications, but where one needs the highest energy density possible, combined with the minimum sensitivity, it would be wise to purify the crystals.
Purification can be done by the following procedure:
The materials needed are high concentration ammonium hydroxide solution (NH4OH) (24% conc. was used here) and glacial acetic acid (C2H4O2) (dilute also works). The two chemicals can be seen next to a 50mL beaker containing the crude mercury fulminate from the previous procedure.
First the mercury fulminate is dissolved in 10 times its volume of ammonium hydroxide (in this case 10mL were used). It forms into a gray solution, with a small amount of precipitate at the bottom. Care should be taken during this procedure to avoid the ammonia gas emanating from the solution.
Once the mercury fulminate had been fully dissolved in ammonium hydroxide solution, the solution was filtered and the filtrate, containing a small amount of metallic mercury and dark impurities (which proved to be almost as explosive as the primary explosive itself) was discarded, whilst the filtered solution was kept.
To the filtered mercury fulminate/ammonium hydroxide solution glacial acetic acid was added drop wise until the pure mercury fulminate crystals started to precipitate out of the solution (approximately 6ml were needed for this). Than more acid was added and the PH was checked until the solution tested neutral. To this solution, an extra 20mL of distilled water were added, and the solution was finally filtered, and washed with an extra 10mL ethanol for quicker drying times.
Here we see the final, purified product. It consists in a regular mass of perfect orthorhombic crystals, and is perfectly white due to lack of impurities. Yield here is estimated at about 2.5 grams (one cc), enough for a #8 blasting cap. The purified product offers several advantages over the impure version: for one, its smaller, uniform crystals pack to a much higher density, providing both more energy and detonation velocity, as well as minimizing crystalline lattice stress, which is a major source of explosive instability. The higher purity should also minimize potential incompatibility and long term stability problems. This explosive is most often used mixed with 10% potassium chlorate by weight, which gives it a better oxygen balance and thus power.
Decomposes (explodes) at 150 ï¿½C.
Molecular mass: 284,62g/mol.
Vdet = 4000m/s at nominal density (2,5g/cc).
= 5000m/s at max density (4,0g/cc).
Very sensitive to shock, friction, and static discharge.
Silver Fulminate Video
The explosive is very sensitive to shock, friction and heat, exploding violently when ground hard between two solid surfaces or when struck by a solid blow between two hard surfaces. Upon burning, very small amounts produce a bright white flash of light and a subsonic air displacement. Burning more than a few hundred milligrams results in DDT (Deflagration into Detonation Transition) and causes a hypersonic shockwave. Everything around the explosive is stained by atomized metallic mercury, and a toxic cloud of the vapor is seen around the detonation site, which should be avoided at all costs.
Its long term stability is fair, the explosive is practically non-hygroscopic and can be safely stored for up to a year so long as it is not allowed to remain in a warm environment or contact materials such as aluminum, magnesium, zinc, copper, brass, or bronze, with which it causes corrosion by formation of amalgams (a more serious problem with unpurified fulminate which contains traces of lead). Long term storage in warm environments renders the explosive useless. For safety of storage the explosive crystals should always be kept under distilled water.