[alt-photo] Re: "Expired" dichromate

[Judy Seigel]

On Mon, 3 May 2010, Tomas Sobota wrote:

> Actually, for a chemical in solution, diluted or not, to degrade with
> time there has to be also a (photo)chemical reaction going on, as for 
> example if there are organic impurities in a dichromate solution. Mere 
> dilution has no effect on how well a chemical keeps, and my example of 
> seawater is as good a proof as any.

Tom, I'm so naive in the issues at issue as to see your comment above as 
assertion, rather than "proof"... Have we tested the solutions? If so, 
what are the findings?  You seem to know far more about the "science" than 
I do.  Still, especially in a case with as many possible variables as, for 
heaven's sake, SEA WATER, some actual tests (under controllable 
conditions) seem called for ....  Tho unless you have a test performable 
by a civilian without special lab equipment for level of salt in water or 
other effects affected thereby, something easier to measure than strength 
of salt solution seems preferable.

I could of course accept your assertions as given & fuggedaboudit.  But, 
alas, my curiosity (famous cat killer) is piqued, so I look for a simple 
test -- an actual TEST of the principle. Since I don't know how to measure 
strength of sodium chloride (though presumably you do ?), I figure 
something other than salt, measurable without special equipment, perhaps 
by eye, like depth of color (maybe tincture of iodine ?), or pH testable, 
would work. Any suggestions?

My original statement, btw, about "keeping" had no time frame.... I often 
keep my dichromate solutions (for instance) for years.  (In fact they SEEM 
to last indefinitely.) The dry ammonium dichromate I'm using now came from 
a lab at school being closed down, tho the bottle looked circa 1920. We 
may not have 90 years to settle this, however... How about a month to wait 
for a *change* ?

PS. I generally use tap water for mixing, unless distilled is specifically 
called for, and my studio isn't quite hospital clean, so some unscientific 
conditions may obtain.  Still, there ought to be a way to test the point, 
beyond (ahem) simple ASSERTION !!!  Any suggestions?

PPS.  I don't know about your house, but in my house, "organic impurities" 
are everywhere..

PPPS. Where does the salt in sea water come from????

J.