Re: Ammoniacal Silver - Safety Concerns

From:"Bryan Llewellyn"

The following text is extracted from Carleton's Histological Technique, 4th
ed., 1967. pp136. by R.A.B. Drury and E.A. Wallington.  The reference at the
end gave anecdotal evidence of several explosions.  It also documented that
ammoniacal silver solutions with metallic deposits, whether on the glassware
(silvering) or floating on the surface are very dangerous as the silver
material is the explosive compound. (silver azide, I believe).   Leaving
silver solutions in sunlight apparently increases its formation, but
refrigeration and the dark do not stop it forming.  Silver solutions should
be made up just before use and discarded immediately after, unless keeping
them for a specified period is required by the technique.  In that case, it
might be advisable to consider changing techniques.  The sodium chloride
solution referred to was 20% aqueous, to ensure an excess.

Bryan Llewellyn

"Finally, all users should be made aware of the potentially explosive
properties of ammoniacal silver solutions. Serious accidents have occurred
from the misuse of this reagent, although receiving little publicity.
Stewart Smith (1943) described such as accident, Nauta and Gygax (1951)
warned of the dangers and Wallington (1965) gave accounts of several
accidents, explained the probable cause of the explosions and offered advice
on safety.
This is as follows:

1.   All ammoniacal silver solutions should be prepared immediately before
use, in clean vessels and not in 'silvered glassware' which is especially
dangerous. Flexible plastic containers offer greater safety. The
recommendation of Lendrum (1947) to coat staining jars with black paper,
bound with strong tape (for storage of solutions) might lessen the effect of
an explosion but would not prevent (at least) subsequent blackening of
person and surroundings.

2.   Solutions should never be exposed to sunlight.

3.   Any unused reagent should be immediately inactivated by the addition of
excess dilute hydrochloric acid or a solution of sodium chloride, and
discarded. Refrigeration does not prevent formation of the explosive

4.   All new staff and students should be instructed in the above."

Wallington, E. A., (1965).
Journal of Medical Laboratory Technology, v22, p220

----- Original Message -----
From: "Kelly Booher (by way of Histonet)" 
Sent: Thursday, August 07, 2003 7:08 PM
Subject: Ammoniacal Silver - Safety Concerns

> In reviewing our procedures, we recently came across a
> warning in the latest Freida Carson book regarding the
> potential explosivity of ammoniacal silver, as is used
> in Gomori's Reticulin staining.  We have in the past
> reused the ammoniacal silver solution for up to one
> week, refrigerating it between uses.
> What are the protocols for dealing with this
> substance?  Are you reusing the ammoniacal silver, or
> preparing it fresh each time?  How are you disposing
> the waste?  Should we be treating the solution by
> precipitating out the silver prior to disposal?  Does
> anyone have a procedure for this?
> Thanks in advance.
> Kelly Booher, BS, HTL (ASCP)
> Anatomic Pathology
> Swedish Medical Center, Providence Campus
> Seattle, WA  98122
> __________________________________
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