>A number of years ago (9 to be more exact) I made a large batch of
>phosporic acid using the standard recipe.  The acid worked well, but two
>years ago it started spending most of its time in a solid state rather than
>liquid.  This reqired that the acid be heated before use so that it could
>be pipetted.  After a about an additional 6 month the glass container in
>which the acid was stored burst in the oven (and what a mess that was).
>After so many years the acid had dissolved more than half of the glass and
>rendered the container too weak.  I now assume that the problem with the
>crystallization of the acid was due to the presence of a substantial amount
>of Si in the acid.  I have been tolds that poly bottles will last an even
>shorter lenght of time, so I quess the message here is that big batches are
>fine, but don't make them so big that the shelf life approaches a decade.
>I also wonder if this is a photo induced reaction, so keeping the acid in a
>dark place might help.


Use teflon storage bottles (PTFE). Keep in warm oven (70 deg C) to allow
easy pouring. Crystallization will occur over time in teflon as well. Only
make enough acid to last 6 months, and lose the hydrogen peroxide!

-----------------------------------------------------
Bob Fifer
Brown University                E-mail: [log in to unmask]
Providence, RI 02912            Geological Sciences

Phone:  401-863-1698
Fax:    401-863-2058