Dear  Lois:

To degas  reagent Ag3PO4, I heated it at 500 C for one hour and kept it in a
regular glass vial for half year. It still kept  its yellow color.

Regards.

Dachun Zhang
Global Geochemistry Corp.

----- Original Message -----
From: Lois J. Roe <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, May 06, 1999 3:01 PM
Subject: Is Ag3PO4 *really* photoreactive?


> Dear Andrew and others:
>
> In response to your comments and because I've been wondering about this
> for quite a while now, I would like to offer the following observations
> for discussion and feedback.
>
> I have read in quite a number of places that Ag3PO4 is photoreactive -
> that it darkens on exposure to light. Having now made oodles and oodles
> of the stuff over the last 10 years, I must tell you that this does
> not completely jive with my observations. I have some pure canary yellow
> Ag3PO4 stored in colorless glass vials that has remained pristine canary
> yellow for years. This is generally stuff I have made from very clean,
> uncomplicated sources, such as CaHPO4 and KH2PO4. I have also produced
> Ag3PO4 that has precipitated out yellow-green *from the beginning of
> precipitation* that has indeed darkened in light. This latter Ag3PO4 is
> generally from less pure phosphate sources, such as NBS-120c.
>
> My guess is that the darker Ag3PO4 is actually Ag3PO4 with some AgNO3 (or
> perhaps something else - whatever it is, it seems to be oxygen-bearing)
> trapped in it - and that it is the AgNO3 NOT Ag3PO4 that is darkening.
>
> In other words, my suspicion is that the ages-old wisdom of some chemical
> literature may actually be mistakenly based on analyses and
> observations of IMPURE Ag3PO4, which I have found is alarmingly easy to
> produce.
>
> I would LOVE it if someone could either refute or substantiate my
> suspicion.
>
> Lois
>
> Lois J. Roe
> University of California
> ESPM/Division of Ecosystem Sciences
> 151 Hilgard Hall
> Berkeley, CA 94720
> Office: (510) 643-6910
> Fax:    (510) 643-5098
> E-mail: [log in to unmask]
>