Re: disposal of formalin

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From:"J. A. Kiernan" <> (by way of histonet)
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On Mon, 20 Dec 1999, Linda Banks wrote:

> I am reviewing our procedures for the disposal of formalin, xylol and
> alcohols.  Can others tell me how they are dealing with these chemicals and
> perhaps give me some references.  Thanks!

 Here is a repeat of a message I sent to HistoNet about a year
 ago, replying to a related question. It relates only to formalin,
 and a one-line summary would be: Neutralize it with ammonia.
 There is a reference to a book about formaldehyde.

  Neutralization of formalin with ammonia

  6CH2O     +     4NH3     =     C6H12N4    +    6H2O

  6 * 30.03       4 * 17.03
   = 180.18        = 68.12        140.19   grams

  180 g CH2O are contained in  180/0.04
             = 4500 ml of 4% (=0.04g/ml) solution (10% formalin)
  68 g NH3 are conmtained in  68/0.27
             = 252 ml of 27% (=0.27g/ml) solution (strong ammonia)

  Therefore 1000 ml of 10% formalin (= 4% formaldehyde) reacts
  with 56 ml of strong ammonia solution, generating 31 g of
  hexamine (in an approximately 3% solution).

  The MSDS for hexamine has all the usual dire warnings,
  relating to the solid. Various LD50s range from 250 to 9500 mg/kg.
  The sheet for hexamine mandelate (the salt used therapeutically
  as a urinary antiseptic) contains much less information, and
  doesn't have nearly so much in it. Hexamine and its salts
  are slowly hydrolysed, releasing formaldehyde, and this
  reaction, which is speeded up by acids, is probably the basis
  of the antiseptic properties.

  The proper name for hexamine is hexamethylenetetramine, and it's
  also commonly called methenamine. The Merck Index lists many
  other synonyms. For more information see Walker,JF (1964)
  Formaldehyde. 3rd ed. New York: Reinhold and London: Chapman & Hall.

  What I do is add about 50 ml of strong ammonia to a container
  with a specimen in a litre or so of formalin fixative, but the
  lid back on, give the pot a swirl, and wait for half an hour or
  so (the reaction is much faster, so the wait probably isn't
  really needed.) The smell of formalin is greatly reduced or
  replaced by a faint whiff of ammonia.

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

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