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Chemicals - shelf-life?


#1

Dear Orchidians, I would be very grateful if any subscribers who are
chemically minded would be kind enough to let me know if there is a
standard shelf-life for chemicals in general or whether each chemical
has a specific shelf-life? I am sure each varies and substances like
acids are different from other types of chemical, but perhaps there
is a standard time, after which it is recommended to dispose (another
matter that is of importance) of the old and buy new chemicals.

I am particularly interested in:

Nitric acid (con & dilute)
Sulphuric acid (von and dilute)
Methylene Iodide
Benzyl benzoate
Bromoform
Monobromonapthalene
Ether
Amyl acetate


The liquids used in developing film!

I have looked at the MSDS (material safety data sheets) for various
chemicals and this does not appear to be given, so any
help would be appreciated by me and I am sure others who use such
chemicals.

Thank you - Nick


#2

Different chemicals have different “shelf lives.” But this "shelf
life "concept usually depends to a considerable extent on just how
pure the reagent is to begin with, and how pure you need it to be
fore your particular use, and whether it has been dissolved (if a dry
chemical) or diluted (if a liquid) an so on and so on.

Nitric acid (con & dilute), Sulphuric acid (von and dilute) 

You probably wouldn’t have any trouble with shelf life with these
two.

Methylene Iodide, Benzyl benzoate 

I’ll pass to John on these two!

Bromoform 

This I wouldn’t keep around for too long. Realize that the fumes can
be quite poisonous to breathe!

Monobromonapthalene 

Pass

Ether 

If you’re talking about diethy ether, I hope you realize that this
one, when sitting, can build up explosive substances in it that just
a jarring can set off. Also it is quite flammable, just a spark can
set it off. The container needs to ALWAYS be grounded, and it needs
to be kept in a hood with an explosion-proof motor in it. I wouldn’t
keep this one around for long. Isn’t there something else you can
use instead? What are you using it for?

Amyl acetate 

Pass. (But I don’t like it!)

I’m trying to figure what on earth you would be using this stuff
for!!!??? Many are quite dangerous if you don’t know just what you
are doing!!!

The liquids used in developing film! 

This depends to a great extent on – what kind of film? AND Which
particular solutions are they? When you say “the liquids used”, I am
assuming here that you mean the kits you may buy to process film in.
Your best bet here is to contact the manufacturer of the kits.
Developers don’t keep for long in liquid form. The air in the
solutioin (and in the bottle if not full) will oxidize the developing
agents. Things like stop baths are usually just dilute acetic acid
and will keep indefinitely. Fixing baths – if it uses an ammonium
hypo, such as in the quick fixers, they can decompose (precipitating
out sulfur) fairly quickly, once they have been used. Sodium hypos
last longer, but will also precipitate out sulfur eventually.

If, on the other hand, you are talking about the liquid chemicals
that you use to hand-mix the sollutions; they are mostly pretty
stable. The dry chemicals are also mostly pretty stable, except for
the developing agents, which will oxidize (and thus lose “strength”).

HTH.

Margaret


#3

Nick, There are other experts that can better respond perhaps, but I
believe that the manufacturers of materials are the sole specifiers
of their products’ shelf life. It depends heavily on the type of
material (I believe polymers are the worst), packaging, stocking
philosophy (if the manufacturer keeps it in stock a long time, they
may consume much of the shelf life themselves), etc.

In my personal experience with photo chemicals, the expiration dates
were stamped right on the containers. Obviously that is not the case
in your situation and I am unable to suggest any other approach
besides contacting the manufacturer.

Good luck,
Tom


#4

Margaret,

Thank you very much for your informative answer and thank you Tom as
well for your suggestions.

The liquids are all used to varying degrees in gemmology and
assaying and can be found in most, if not all, gemmological
laboratories. Some are used on a fairly regular basis and others less
regularly so often tend to be tucked away in a cupboard just incase
the need arises! As far as I know, some of these liquids can also be
bought from the GIA (GI) and other gemmological equipment suppliers
and are often mixed in heavy liquid preparations for density
determination. I personally try to avoid using them for the reasons
you state, but sometimes the need does arise.

I do have the MSDS for most of these liquids, so am
aware of the dangers and precautions however I do not have an
accurate idea of how long one is required to keep them before
renewing?

I think that I shall have to find a suplier in our area and ask them
directly, however I just thought that the font of knowledge here
would be able to assist and of course I am glad that I asked as I
have indeed learnt something from both of the replies I have
received. This is exactly what Orchid is all about!

Kind regards - Nick


#5

OK, Nick. The main one to be concerned about would be the ether. If
you don’t use it often, it may just be best to buy a small amount
when you need it, and discard the rest after you finish that
particular project. But – just as an example that this needs to be
taken seriously – One time I came out after watching a Shakespeare
performance in the theater at Southern Utah University. I started
walking to my car, which was parked on the street in front of the
Science building. But the street had been blocked off, and also the
sidewalk – I was stopped by the police and told I would have to
wait. Someone had discovered a suspect old can of ether in one of
the labs in the building. They had evacuated the entire area and
were allowing nobody in. The police bomb squad had been called to
come and gingerly remove it and dispose of it safely. So I had to
wait several hours before I could go on home.

This hazard is something you might call to the attention of the GIA,
and suggest that they might find a less hazardous material to
substitute for the ether.

Good luck!
margaret