[meteorite-list] Scales

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sun, 10 Dec 2006 00:11:08 -0600
Message-ID: <007a01c71c21$fd2b7290$a925e146_at_ATARIENGINE>

Hi, All,

    While not the answer to the question of how
to get a dirt-cheap, pocket-sized, deci-milligram-
accurate scale that will weight a 50 lb Campo,
you might consider a purely mechanical, quartz
fiber torsion balance scale of some antiquity.
I guarantee you that such a purely mechanical
scale will not be influenced by light bulbs, fluorescent
or incandescent, radio waves, tv sets, nor any
other electromagnetic device smaller than a cyclotron.

    The invention of the torsion balance is commonly
credited to the English geologist John Michell, who
made his instrument c.1750, and to the French
physicist Charles A. de Coulomb, who independently
devised such a balance c.1777 and used it to measure,
well, the Coulomb. Henry Cavendish used one to
weigh the Earth (measured the force of gravity of
a nearby heavy object on a small object attached
to the balance.)

    For a century, pharmacies who compounded
medications needed the ability to weight quantities by
the milligram with accuracy. The vast majority of
them used scales made by the Torsion Balance Co.
of Clifton, NJ (founded 1897, now Fulcrum, Inc.,
with scales sold under the brand name Torbal):
http://fulcruminc.net/sub/aboutus.html
     The standard was a scale with 0 to 120 gram
capacity with +/- 0.25 mg accuracy, a standard
enforced by most States' Boards of Pharmacy.
New ones are expensive, but old ones are not.

    Purely mechanical, they are calibrated by being
leveled with three micrometer screws on which the
balance contacts the surface it sits on. You can
calibrate one in a few minutes once you get the
hang of it. They are sensitive to vibration, though,
and need a stable place to be used.

    Since my family owned and operated pharmacies,
I ended up with one (no, I'm not trying to sell it)
made by the Torsion Balance Co. in 1905. I've
checked it, and it's still quite accurate. I find a fair
number of them on eBay (search for Torsion Balance),
sold as antiques. Because of that "antique" tag, the
newer models, from the 1940's and 1950's, go for
much less than a WWI or 1920's model that are so
much more "quaint" looking. Working ones go for
$50 to $250. Look for one with the weight sets with
it, as the weights often bring as much as the balances.

    But the working lifetime of a torsion balance is
essentially forever, if treated gently and kept in a clean
environment. They should be called "transportable"
rather than "portable." The only time I ever used mine
on a meteorite was when I bought a "one gram" slice
of a Martian from a fossil collector who had bought it
at one of the big shows (Tuscon? Denver?) from a
meteorite dealer who told him that the slice "was about
one gram, give or take the odd ten milligram." He didn't
have any scales, so I bought on the basis of a per gram
price, and I weighed it on my torsion balance.

    The torsion balance said it weighed 0.55125 gram.
"Well, this old thing is way off!" was his reaction. I
calibrated it again and got 0.55150 gram. I had him
weigh some standardized weights (I've got five sets).
He calibrated the scale himself. The little Martian always
sat between 0.55000 and 0.55150 grams. Finally, we
went together to a big commercial jeweler and got it
weighed on a flashy electronic gem scale with bells
and whistles, which said it weighed 0.55136 grams,
give or take the odd 1/10000 gram, and that's what
I paid for. And, no, I don't know which "dealer" he
bought the Martian from; it was a long time ago.
(This is not a dealer story.)

    The point of the story is that purely mechanical
quartz fiber torsion balances are quite accurate and
dependable, even if they've sat unused for 50 of
their last 100 years (like mine had). You DO need
to have a good set of standardized weights to use
with them, as they are pan balances.


Sterling K. Webb
------------------------------------------------------------------
----- Original Message -----
From: "Ed Deckert" <edeckert at triad.rr.com>
To: <trifid at timewarp.de>; <jbaxter112 at pol.net>
Cc: <meteorite-list at meteoritecentral.com>
Sent: Saturday, December 09, 2006 8:42 PM
Subject: Re: [meteorite-list] Scales - Looking for Advice


> Norbert,
>
> I do not have much to back this up, but I have been told that electronic
> scales can be "influenced" by a nearby fluorescent light fixture that has
> been turned on. This would imply that an incandescent light, natural
> sunlight, or some other light source that did not involve the use of
> ballasts or transformers would be the best light source while using such a
> scale.
>
> I have a gram scale that runs only on AC current. It interferes greatly
> with the FM radio reception in my shop whenever I use it. Perhaps the
> actual issue is the fact that my scale is run by AC, and is putting some
> kind of interference back through the electric lines. Or it may simply
> generate some kind of RF interference that travels through the air.
>
> With my scale causing radio problems, it makes sense that a fluorescent
> light could impact my gram scale. I use a fluorescent lamp to illuminate
> my
> shop, and it seems that I have to recalibrate the scale more frequently
> than
> I would expect. But I wonder if the same would hold true for a battery
> operated scale?
>
> Does anyone here have any such experience with this problem?
>
> Ed
>
> ----- Original Message -----
> From: "Norbert Classen" <trifid at timewarp.de>
> To: <jbaxter112 at pol.net>
> Cc: <meteorite-list at meteoritecentral.com>
> Sent: Saturday, December 09, 2006 7:39 PM
> Subject: Re: [meteorite-list] Scales - Looking for Advice
>
>
>> Jim wrote:
>>
>>> I for one would like to hear your final conclusion. I have considered
>>> buying such a scale for some time. I have been too busy, or too lazy
>>> if I am to be honest, to do my homework and would love to benefit
>>> from your efforts. I am sure I'm one of many on the list that has
>>> considered buying a scale so I'm sure others would be interested as
>>> well.
>>
>> Good idea - I will certainly let you and the list know. And as soon as I
>> have my new scale I will test it as I have quite a few samples that have
>> been weighed rather precisely on A grade laboratory scales. So let's see
>> what these "cheaper" portable precision scales can do.
>>
>> This might take some weeks, but I will surely come back to it.
>>
>> All the best,
>> Norbert
>>
>>
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Received on Sun 10 Dec 2006 01:11:08 AM PST