From: Judy Seigel (jseigel@panix.com)
Date: 03/22/02-12:02:18 AM Z
On Thu, 21 Mar 2002, alnovo@inwind.it wrote:
>
> YES, that is a normal laboratory practice for a chemist. I am referring
> to, for example, preparing 1000 ml 0.1N (1 equivalent/litre) silver
> nitrate solution: I need to weight 16.987 grams (up to the milligram) of
> silver nitrate, then I transfer all that stuff to a volumetric flask. I
> will use a funnel on the flask, then using a wash bottle I will gently
> soak the watch glass many times with small amounts of distilled water,
> paying attention also to the opposite side of the glass and the borders.
You're mixing 1.698% solution ????
> If you want to dissolve your substance with a very small amount of
> liquid probabily you have a very small amount of substance too. You need
> to use a watch glass, a vessel and an amount of liquid proportional to
> the amount of the weighted substance.
>
> However, chemists are used to cut an hair in four (or more...).
I'll say...!!
I've measured, for instance, silver nitrate on a piece of paper (as
described) -- maybe 17 or 20 g -- in 100 cc water, which would have made
for some close calls with all that sluicing. On some papers I'd see tiny
black specks after the paper sat around in the light for a few days... on
a smooth vellum or tracing paper I didn't. I took that to mean all the
chemical had slid off. But I expect now you'll tell me some remained just
too small to see :(.
Actually, seriously, I begin to think (having tried some REALLY accurate
tests with cyano) that perfect control -- even I bet in a lab -- is a
chimera... there's always something -- tho maybe in a clean room with
large quantities, and everything, eg., electricity, under strictest
discipline you get closer.
Judy
> think this is the case of the normal photographic practice, with some
> exceptions (gold and platine, for example).
>
>
> Alberto
>
> http://spazioweb.inwind.it/albertonovo/index_eng.html
> http://www.grupponamias.com/novo/index_en.htm
>
>
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