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Jim:
I'm glad we have you with us in this business to set us straight!!
Steve
>Dear Isogeochemists,
>
>CrO3 was added (by McCrea also) to the witch's brew in order to oxidize any
>organic matter present in the commercially available 85%H3PO4 (and the P2O5
>added). The H2O2 used in the old recipe was a REDUCING agent to bring down
>the oxidation state of chromium from +6 down to +3 ( thus the green color).
>
>The advantage we have today is that one can purchase 107% H3PO4 that is very
>pure so that one no longer needs to add the CrO3. So Bjorn, your laboratory
>can now be relatively free of carcinogenic compounds.
>
>Jim O'Neil (from Tuebingen)
>
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Stephen S. Howe Office: (847) 491-8180
Northwestern University Stable Isotope Lab: (847) 491-8182
Dept. of Geological Sciences Geochemistry Lab: (847) 491-8184
1847 Sheridan Road FAX: (847) 491-8060
Evanston, IL 60208-2150 e-mail: [log in to unmask]
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