Dear Marie,

>I have to prepare H3PO4 suitable for conventional CO2 extraction on
>carbonates and have 4 questions concerning the preparation procedure....

If you go to the isogeochem website:

http://beluga.uvm.edu/geowww/isogeochem.html

and search the ARCHIVE using the term PHOSPHORIC you will find that
discussions concerning your queries (and more) took place on the 14 June
1996.

Good luck.
Kevin


**********************************************************
Dr Kevin Faure
Department of Geochemistry
Geological Survey of Japan
1-1-3 Higashi
Tsukuba
Ibaraki 305
Japan


Tel. and Fax: +81-298-54-3726