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]