alnovo@inwind.it
Date: 03/20/02-01:13:45 AM Z
>
>
> On 20/03/2002 05:57 , Judy Seigel wrote:
>
> ... 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.
Those "watch glasses" are used because one can wash them while transferring the chemical to the vessel, to be sure that truly *all* the weighted substance goes into the solution. This is particularly needed for an exact weighting, such as for very small amounts.
I don't like plastic, as very often it is electrized and the powder to be weighted spreads all over the surface and sometimes also out and under the plastic vessel.
It is better -in a domestic environment- an aluminium foil, tissue paper, typing paper or baking paper depending on the nature of the substance. Do not use aluminium or paper for sodium or potassium hydrate, other caustic or higly acidic substances: in these cases plastic and glass are a must.
Alberto
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