Lois Ruben Aronow on fri 4 dec 98
-------------------
....use the darn thing???
Ok, stupid not-so-newbie question. I thought it might not be a bad
idea to have one of these gadgets in the studio and to know how to use
one, even if I never do. BUT - it looks nothing like I expected it
would. Looks like a giant thermometer, in fact. And came with no
instructions. Would one of you kind souls care to shed some light on
this mystery?
Gavin Stairs on fri 4 dec 98
At 10:00 AM 12/4/98 EST, Lois wrote:
....
>Ok, stupid not-so-newbie question. I thought it might not be a bad
>idea to have one of these gadgets in the studio and to know how to use
>one, even if I never do. BUT - it looks nothing like I expected it
>would. Looks like a giant thermometer, in fact. And came with no
>instructions. Would one of you kind souls care to shed some light on
>this mystery?
Hi Lois,
I posted a fairly detailed description of hydrometry not long ago. In it,
I discouraged the use of immersion hydrometers, which is what you've got.
The way it is used is quite simple, but tricky, which is why I discouraged
their use. The simple part is, you float it in the liquid to be measured,
and read the scale where it meets the liquid surface. I don't know what
type you have, so I don't know what scale it reads. The useful ones all
read in density units, like g/cc and oz/fl.oz. If your scale says "degrees
Baume" or something like that, you'll need a table to convert to a useful
unit. Actually, such hydrometers are usually not useful for potting
liquids, as they don't measure dense enough liquids. You want one that
measures between 1 and 2 g/cc, or at least a large fraction of that range.
If you drop it in the liquid, and it falls over, or doesn't stand up
straight, it is either upside down, or has too small a range for the liquid
you are measuring, or...
There is a generic problem in measuring the density of slurries with an
immersion hydrometer. That is, the slurry may tend to set, and hold the
hydrometer up or otherwise interfere with it assuming its equilibrium at
the proper point on the scale. The first thing is to stir vigorously just
before measuring (don't use the hydrometer, as they tend to be delicate).
Then you can try tapping it lightly until it stops moving up or down when
you tap it, or you can take a bunch of readings by dropping it into the
liquid from various heights (not very high: just slightly different, so the
instrument bobs up and down in a different way each time before settling),
and take the median as your final result.
Another problem is that the hydrometer may get coated with the slurry,
which will also give you a false reading, and also obscure the scale. You
might try coating the hydrometer with wax or oil (a light coat).
Hope this helps.
Gavin
Gavin Stairs
Stairs Small Systems (S3)
921 College St., # 1-A
Toronto, Ontario, Canada M6H 1A1
(416)530-0419 stairs@stairs.on.ca
Dennis Davis on sat 5 dec 98
Lois Ruben Aronow wrote:
>
> ----------------------------Original Message-----------------
> Ok, stupid not-so-newbie question. I thought it might not be a bad
> idea to have one of these gadgets in the studio and to know how to use
> one, even if I never do. BUT - it looks nothing like I expected it
> would. Looks like a giant thermometer, in fact. And came with no
> instructions. Would one of you kind souls care to shed some light on
> this mystery?
****
Lois,
Several years ago at the school where I taught we had a disagreement
about the use of the hydrometer. I believe we purchased the hydrometer
from Standard Ceramics in Pittsburgh. I obtained the name of the
manufacturer (I think in California) and phoned them. Here are their
instruction for use.
(1) Stir the glaze thoroughly. Take the reading immediately after
stirring; some glazes settle quickly and you will get a false reading if
you delay taking the reading.
(2) Hold the Hydrometer by the small end and allow it to settle
slowly into the glaze. Release the Hydrometer only when you feel it
will not settle much further. Any dropping of the Hydrometer will
distort the reading. If possible, the Hydrometer should be read while
in the liquid. If the bucket does not contain enough liquid to take a
reading, pour some of the liquid into a tall narrow container to take
the reading.
Hope that helps.
Dennis in Stafford, VA
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