From: Judy Seigel (jseigel@panix.com)
Date: 03/19/02-09:57:43 PM Z
On Tue, 19 Mar 2002, Bob Kiss wrote:
> DEAR JEFF,
> Originally it was exactly what it says...the glass cover over the hands
> of a watch (sometimes called a watch "crystal")...what you look through to
> see the time. All watches still have them but many are now high impact
> plastic. Then it became a generic term for chemists (and biologists) and
> they were created independent of watches specifically for measuring
That's a new one on me... My understanding (& caption in catalog I bought
them from) was that they're made for covering beakers and graduates -- &
very handy they are too. They dip slightly into the opening so don't slide
off readily, & are slightly airtight, chemically neutral & washable.
They also come in different sizes and thicknesses... Maybe they are used
for measuring chemicals, but I wouldn't -- they're generally too small,
especially the itty bitty ones. You'd surely get chemical on the tray, or
I would.
For measuring chemicals IME, the easiest really IS a piece of paper, about
a quarter the size of a sheet of typing paper.. What you do is fold up the
edge on all sides ... about a centimeter (less than 1/2 inch). That
prevents spill ... and the chemical won't stick on smooth paper (I use
typing or tracing paper). When you pour the chemical into bottle or
beaker, gently squeeze the paper in one hand into a loose V shape. This
makes a kind of pouring spout -- so nothing spills.
It also saves work & water: no washing -- for the next chemical you take a
new paper. I usually leave the scale zeroed for that weight, but if you're
measuring a large amount, hardly matters -- less than a gram.
Judy
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