From: Judy Seigel (jseigel@panix.com)
Date: 12/10/01-12:34:51 AM Z
On Sun, 9 Dec 2001, Ted Edkins wrote:
> Judy, Alberto has answered your question about water of crystalization very
You guys who know this stuff think it's more obvious than it is... that
is, I now SURMISE what "dihydrate" means, but couldn't handily use the
concept.
> well. The only thing I'll add is that sometimes in formulae an amount of a
> substance is given but you are not told whether they mean anhydrous or with
> water of crystalization present. This is very confusing as you get
> differing amounts of the substance in the solution. That's one reason,
> amoung others, that chemists use molarity and not percentages.
> I'm often called many things other than a scholar and a gentleman, so thank
> you.
I think they assume in these formulas that you're using the prevalent form
for the period, usually the monohydrate, since (I think) it keeps better.
Anyway, in these processes, I find difference between amounts for mono and
anhydrous are moot. Probably matters in film developers where you're
working strictly by time & formula, but not (I find) where you're juggling
all sorts of variables, including hand coating, and in the light, testing
as you proceed.
> As to glyoxal; I looked at my bottle of Sigma Chemical Co glyoxal at work
> on Friday and it was a wet yellow gunge. I'll bet there was very little
> glyoxal left in the bottle. I'll ask my chemical analysis friends if there
> is a simple method of estimation of the substance which may be of use to us.
> Ted
I have an old bottle of formaldehyde in which the bottom half inch turned
to white powder. (What we really need is to bottle one of your chemical
analysis friends -- except I find our questions seem rarely to be the ones
they have answers to. :(
best,
Judy
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