From: Liam Lawless (liam.lawless@blueyonder.co.uk)
Date: 02/20/03-02:40:08 PM Z
Re: Aqua Regia & safeyHi Sandy,
I don't think Gord's suggestion is about censorship at all, but a sensible
attempt to knock our heads together. So far, there's been no agreement at
all between Dick and myself and the conflicting advice in our separate
postings is of no value if folk don't know what they can trust. And further
postings in similar vein would likewise be futile. That's one reason I've
been keeping quiet as far as possible. But I'm willing to write something
for the archives about my own experience of using aqua regia, which Dick and
I can maybe argue about privately before it sees the light of day. Don't
know that we'll ever agree completely, but we'll see.
As far as I'm concerned, it's not about winning the argument or scoring
points. Better for me, perhaps, that no-one does try it - at least then I
can't be blamed for anything!
Liam
-----Original Message-----
From: Sandy King [mailto:sanking@CLEMSON.EDU]
Sent: 20 February 2003 17:23
To: alt-photo-process-l@sask.usask.ca
Subject: Re: Aqua Regia & safey
Gordon wrote:
On the alt-photo list its assumed that everyone knows how to handle the
potentially dangerous chemicals. When we post a message about salted
paper we don't describe the hazards and necessary precautions to be
taken
when working with silver nitrate. The same for dichromates in gum
printing and so on.
I do not agree that this is assumed, and when it is a matter of safety I
don't think we should every make such an assumption. For example, how many
times have people posted to this list regarding safety issues relating to
the use of dichromates? But dichromate and silver nitrate, to deal only with
the two chemicals you mention above, are not hazardous in common use.
Obviously you don't want to ingest them but in common use and storage they
are not going to explode in your face and kill you
If people are unwilling to do this then I would insist that the issue of
Aqua Regia safety should no longer be discussed on this list.
I would hope that those involved in the aqua regia issue would present a
report on the safety issue, as you suggest. However, as a very long-time
member of this list I am extremely concerned that you would suggest
censoring discussion of aqua regia when we have never attempted to limit
discussion of other far less hazardous materials. It would set a dangerous
precedent and suggest a decision made for reasons other than the general
interest of the list. I am no expert on chemical safety but even a cursory
reading about aqua regia clearly suggests that its presents a hazard quite
beyond that of most of the chemicals we use in alternative photography. So
if you prevent people from talking about aqua regia here, where will you
draw the line with other less dangerous chemicals? Do you also propose to
prevent discussions of daguerreotypes because they involve mercury, or
warnings about the dichromates, chrome alum, and such?
Sandy King
Thanks
Gord Holtslander
List Manager
On Mon, 10 Feb 2003, Richard Sullivan wrote:
> Subject: Kitchen brewed gold chloride! Not!
>
> Several years ago there was a brouhaha here over an article in Post
Factory
> No 3 on making gold chloride in your kitchen or darkroom.
>
> The issue at hand was safety. I believe some correction were made in
No 4
> but the problem still exists as many here might read No. 3 without the
> benefit of the corrections in No 4. It is highly doubtful that anyone
would
> try this trick at home but someone just might as the article proposes
just
> such a project.
>
> Several had said here that aqua regia would not explode in closed
> containers. Wrong!
>
> Liam Lawless, author of the article, said the following June of 1999
on the
> list via another members repost or forward.
>
> Liam says:
>
> >We have perhaps been remiss in implying that this process can be
carried
> > >out indoors, which it definitely should not without the proper
equipment,
> > >etc., but the only other point that gives me real cause for concern
is your
> > >assertion that stored aqua regia could explode.
>
> Not only my assertion but that of the American Industrial Hygene
Association!
>
> >I have, therefore, spoken
> > >to a chemist about this today (whose name I shall not give as he
has
> > >nothing to do with this debate, but who has some interesting views
on
> > >safety and responsibility that I hope he will one day share), and
the gist
> > >of what he told me is as follows.
> > >
> >Aqua regia is a stable mixture of acids that will not spontaneously
explode
> > >at normal temperatures, though a small amount of pressure will
build up in
> > >its container until any air present is saturated with the acid
vapours. It
> > >should, of course be kept in a glass or plastic container with
screw cap,
> > >which is capable of withstanding the small build-up of pressure
that
> > >occurs. And the general rule for acids is that they should be
stored in a
> > >cool, dark place; heat increases the pressure, and light may cause
> > >photolysis that in turn causes decomposition and the liberation of
gases.
> > >It is also important that the container is clean, to avoid
contaminants
> > >that could catalyse decomposition.
>
> This is patently wrong and compounds the error in PF No 3.
>
> To add to the warnings I have found the following at:
>
> http://www2.umdnj.edu/eohssweb/aiha/accidents/explosion.htm#Two
>
> Do a page search on "aqua regia" as the pertinent part is about 80%
down
> the page. It is from the American Industrial Hygene Association on the
New
> Jersey Medical and Dental College site. It highlights two cases of
aqua
> regia explosions. These were not just caps blowing off but violent
> explosions shattering the glass bottles with enough force to break
other
> nearby bottles. Had someone been in the room and been the subject of
flying
> glass and hot aqua regia spray it could have been very messy.
>
> The text follows:
>
> >Two Explosions Involving Aqua Regia (top)
> >Key Learning Points
> >1. Use a reagent that is milder than aqua regia for cleaning
glassware if
> >it will suffice.
>
>
>
> >2. Do not take aqua regia out of the fume hood in which it was
prepared,
> >and do not store it there either; make only what you need and destroy
the
> >residue. Aqua regia can be destroyed by cautious and careful dilution
with
> >water - talk to your supervisor or your safety office for a detailed
> >procedure. If necessary, the solution can then be neutralized and
disposed
> >of in the approved manner.
>
>
>
> >3. Never put aqua regia in a closed container or near flammables.
>
>
>
> >There have been explosions involving aqua regia ( a mixture of
> >hydrochloric acid and nitric acid) reported at two universities. Both
of
> >the incidents took place in chemistry laboratories.
>
>
>
> >In the first incident, a graduate student was using aqua regia for
the
> >cleaning of NMR tubes. When he was finished, he placed the residues
(about
> >50-60 ml) in a 4 litre waste bottle, capped it tightly and placed it
in a
> >flammable storage cabinet. Approximately one hour after the bottle
was
> >placed in the cabinet, it burst, breaking an adjacent bottle of
pyridine.
> >Luckily, the pyridine did not ignite and other nearby bottles
containing
> >flammable solvents did not become involved. The pyridine leaked onto
the
> >floor, where it dissolved floor tiles and created a lingering bad
smell.
> >The second incident occurred in a fume hood in a synthetic chemistry
> >laboratory. A tightly closed waste bottle containing used aqua regia
> >exploded, most probably due to pressure buildup inside the bottle.
> >Since the sash was not completely closed the broken waste bottle was
not
> >contained. Broken glass as well as some liquid acid waste were thrown
out
> >of the hood. Since nobody was near the hood at that moment, there
were no
> >injuries. Moreover, a nearby bottle of mercury nitrate waste was also
> >broken as well as the secondary container, so that a small spill
(less
> >than 1 liter) of liquid acid and solid mercury nitrate occurred
inside the
> >hood.
>
>
>
> >What is aqua regia?
> >Aqua regia has been used by chemists for centuries, especially as a
medium
> >for dissolving noble metals but also for other purposes. It is a
mixture
> >of concentrated hydrochloric and nitric acid which forms a powerful
> >oxidizing medium. Mixing an oxidizer with organic materials may
result in
> >a highly exothermic reaction. Even without other materials present, a
> >chemical reaction occurs slowly and brown fumes of NO2 can be
observed (in
> >freshman chemistry terms, nitric acid is reduced and hydrochloric
acid is
> >oxidized). The activity as a dissolving agent decreases slowly and
so, by
> >definition, the solution is unstable - it should be used "freshly
prepared".
>
>
>
> >Rules for using aqua regia
> >Aqua regia is often used as a substitute for chromic sulfuric acid
> >cleaning solutions. However, aqua regia is also corrosive and
strongly
> >oxidizing. It is essential for some purposes but should not be used
for
> >routine cleaning of glassware. If a milder reagent will suffice avoid
> >using aqua regia. Alternatives include ultrasonic baths, alconox or
> >similar detergents, Pierce RBS-35 (available from VWR) or similar
> >detergents or biodegradable surfactants.
>
>
>
> >Be aware that sufficient pressure can build up in a short amount of
time
> >to burst the container, even from a very small volume of aqua regia.
>
>
>
> >If it is decided that aqua regia is needed, wear protective clothing
> >(goggles, gloves, coat) and work in a clean well-ventilated fume
hood.
> >Keep the sash down when reactions are in progress.
>
>
>
> >Never take aqua regia out of the hood.
>
>
>
> >Prepare it, use it, and destroy any excess in the hood in which it
was
> >prepared.
>
>
>
> >
> >Only prepare the amount of aqua regia you need for immediate use.
Never
> >store it and never put it in a closed vessel, since evolved gases
will
> >cause a pressure build-up and possible explosion.
>
>
>
> >Aqua regia is a strong oxidizer. It is incompatible with organic
solvents,
> >flammables and any reducing agents.
>
> --Dick Sullivan
>
>
>
---------------------------------------------------------
Gordon J. Holtslander Dept. of Biology
holtsg@duke.usask.ca 112 Science Place
http://duke.usask.ca/~holtsg University of Saskatchewan
Tel (306) 966-4433 Saskatoon, Saskatchewan
Fax (306) 966-4461 Canada S7N 5E2
---------------------------------------------------------
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