From: Sandy King (sanking@CLEMSON.EDU)
Date: 02/20/03-11:22:39 AM Z
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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