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Re: PCB Question

Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dunckx-at-freeuk-dot-com>

Hi David, All!

>I've read that you can drop a drop of the fluid in question into
>some water and if it floats, then in isn't PCB, as PCBs have
>a higher specific gravity than water. However, I personally do
>NOT suscribe to this as a sure-fire way to detect the presence/
>absnece of PCBs as they may very well be mixed in with petro-
>leum oil, which of course has a lower specific gravity than water.
>Maybe some of the resident chemistry majors could comment
>on this?

This is a difficult one because without access to the sort of gear you
find in an analytical lab, there is no sure-fire way I can think of
which is guaranteed to be reliable and of course given the toxicity
and illegality of PCBs, reliability is naturally the thing you want .
. . <gotcha>

The one test we used which is normally OK (but subject to false
positives) is the copper wire test.  If you put a clean, bright copper
wire into a hot gas flame (the non-luminous blue kind, as from a
bunsen burner or blowtorch - no, you don't do this in the kitchen on
the gas stove) there may be a transitory greenish flicker, but after a
few moments the flame will remain colourless.  If you now dip the same
wire into straight oil and repeat the process, there will be a
momentary smoky flame and nothing much else.  But if the compound on
the wire contains halogen (fluorine, chlorine, bromine, iodine) these
help volatilise the copper, and you will get a greenish flame which
persists for a few moments.  Best seen in dim light.

It isn't totally foolproof, but it's the best I can come up with.
Note - this test applies to organic materials, inorganic materials can
do some strange things - sodium chloride will of course obscure the
green with sodium yellow.  If you want a "standard" to compare with,
shred some PVC finely and use that as your comparison.  Heat the wire
as above and dip into the PVC shavings so they melt on the wire (you
don't need much, if you can see it, it's probably enough) and pop it
back in the flame.  The chlorine content of the PVC should show you
the sort of result you are looking for.  You'll then need a clean
piece of wire, or hold the existing one in the flame until it clears,
before testing your suspect oil.

Not 100% guaranteed, but hope this is of use.

Geek#1113 (G-1)