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Re: mercury amounts & repairs



On Sat, 17 Feb 1996, neonthom@earthlink.net wrote:
>I seem to have been getting a lot of repairs in lately w/ huge amounts of
>mercury in them.  Some of the units I've seen have the amount of about two
>eraser heads or more.  These units don't seem more than 8-10 feet.
>
>I'm used to putting in an average of the size of a large pin-head; plus or
>minus depending on the size of the unit.  I find the literature that I've
>read about amounts to only refer to measured amounts and at this time I
>don't have a way to measure other than eye-balling it.  I do understand
>that in this case more is not better, but with the amounts I see some
>people putting in, it has made me wonder.
>
>Does anyone have any feedback...?

>NeonThom
>
The method I use to add mercury is as follows. I'd appreciate comments ..

Samuel C. Miller wrote in "Neon Techniques & Handling" page 189 to use 600 
milligrams of mercury for a tube greater than 4 feet in cold weather -- 400 
milligrams for greater than 4 feet in warm weather -- 400 milligrams for short 
tubes in cold weather -- and 300 milligrams for short tubes in warm weather.

We know that there are 13.5 grams per cubic centimeter of mercury (it's specific 
gravity). Since I use 5 mm glass (with a trap) to connect to the tubulation, we 
can calculate what LENGTH of mercury in 5 mm glass weighs the 300 to 600 
milligrams that Miller suggests.

Most 5 mm glass has a mean wall thickness of about 0.045 inches so the inside 
diameter is about 0.2714 cm. That calculates to an inside area of 0.058 square 
cm.

So -- if we ignore the meniscus (as a little extra for the pot) -- 300 
milligrams of mercury will occupy 3.84 mm in a 5 mm tube -- 400 mg occupies 5.12 
mm -- and 600 mg takes up 7.69 mm.

While injecting the mercury, I hold a scrap piece of 5 mm glass perpendicular to 
the input side of the merc trap. A length of mercury in the tube about equal to 
he OD of the 5 mm tube is about 400 mg. A scrap piece of an 8 mm tube would be a 
pretty close gauge for 600 milligrams.

I think this is a little better than "eye-balling it".

Best regards -- Jack