This is very good information.  I recommend the bottles be opened underwater if
the picric if dried.

Rande Kline, HT (ASCP)
Technical Services
EM Science/BDH





"J. A. Kiernan" <jkiernan@julian.uwo.ca> on 01/24/2000 11:05:35 AM

To:   histonet <histonet@pathology.swmed.edu>
cc:   "Hagerty, Marjorie A." <mhagerty@emc.org> (bcc: Rande Kline/EMI/Merck)
Subject:  Perceived dangers of picric acid and Bouin's fixative




  Some recent HistoNet questions and answers cry out for
  an explanation of why the use of picric acid (trinitrophenol)
  is less perilous than some laboratory workers believe.

  This compound was the high explosive used in shells before
  and during the First World War. In 1915 the largest man-made
  non-nuclear explosion occurred when a French freighter, the Mont
  Blanc, full of old picric acid being brought to Canada for
  disposal, caught fire in Halifax Harbour. Many lives were lost
  and buildings demolished in the city: good reason for picric
  acid's bad reputation.

  Like other high explosives (TNT, ammonium nitrate etc), and
  unlike the compounds used in detonators (such as mercury
  fulminate) picric acid must be brought to a high temperature
  to make it explode. That temperature is 300C. The melting
  point is 123C. Shells containing picric acid did not usually
  explode in response to the impact of the propellant in the
  gun. Picric acid is always stored mixed with at least 10%
  of water - preferably more than that - so its temperature
  can never rise above about 100C. There is a risk that a tiny
  bit of the dry picric acid around the neck of the bottle might
  be brought to 300C by friction when removing a tight cap
  or stopper. If the cap doesn't come off easily it is wise to
  stand the bottle upside down in water for half an hour or so,
  to wet and dissolve the picric acid around its neck.

  It is important to check jars of picric acid regularly to
  make sure there is always water above the level of the
  powder.

  Picric acid is not very soluble in water (1.28% at 20C), so
  aqueous solutions like Bouin's fluid are not explosive hazards.
  Saturated alcoholic picric acid (contains 8.3%) should be
  treated with more caution because the solvent is flammable.

  Ammonium picrate (which was used in some traditional staining
  procedures) is much more sensitive to percussion than picric
  acid.

  There is also a toxic hazard. Picric acid can cause a rash if
  it gets on the skin of susceptible people, and a variety of
  symptoms, mostly gastrointestinal, if it is ingested. Oral
  LD50s reported in various animals range from 100 to 250 mg/kg,
  suggesting that a fatal human dose might be about 7 gm of
  the solid or 550 ml of a saturated aqueous solution.
  Systemic toxicity is therefore unlikely to be encountered
  unless someone tries picric acid, which has a strong bitter
  taste, as an unusual way to commit suicide.

  There is no shortage of tales of explosions involving picric
  acid in labs but these always seem to be second-hand (or more
  likely 5th or 6th-hand), like ghost stories, and are not
  convincing. This danger exists only for a bottle of the solid
  that has dried out and is then greatly heated or subjected
  to a shock greater than that of being shot out of an
  artillery piece.

  I hope this information (derived from an organic chemistry
  textbook, a U.S. Government web site and the Merck Index)
  will convince lab workers in histology & pathology that
  solutions containing picric acid, including Bouin's
  fixative, are no more dangerous than many other things
  used in labs. Sharp blades, shards of broken glass and
  boiling water are much more likely to cause serious
  injuries.

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1