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Hi Glen!

I don't think your boss looked very hard.  I have personally described our
method for making 100% phosphoric acid several times on Isogeochem over
the past 5-8 years.  I am not in my office today, so I can't give you all
of the details, but essentially, I take 85% phosphoric acid from Fisher,
heat it in a round-bottomed flask to "steam" the water off (don't boil it
or it will polymerize later on cooling) for about 2-3 hours until no more
water vapor comes off and the volume has reduced by about 20-30%.  I then
cool the acid after stoppering it in the flask overnight.  The next
morning I check the specific gravity.  Although the optimum s.g. is 1.92,
an s.g. of about 1.88-1.89 works better for our MultiPrep system so that
the acid doesn't take more than about 15 minutes for about 4 droplets to
pass through the silica capillary used in our system.  I then store this
acid in a tightly sealed amber bottle.  I have never needed to place a
vacuum on the acid or store it under helium or nitrogen.  The 300-400 mL I
make at a time routinely keeps for a year without any problem.

Steve

Glen E Martin said:
> We are looking for a method to make 100% phosphoric acid without using
> phosphorus pentoxide or chromium oxide.
>
> My boss has checked the archives and has not found a method. He suggested
> a vacuum distillation method.
>
> A method of preparation or a source of the 100% phosphoric acid made
> without phosphorus pentoxide or chromium oxide is needed.
>
> I would appreciate help.
>
> Thank you.
>
> Glen


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Stephen S. Howe                         Office:  (518) 442-5053
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