MadSci Network: Environment & Ecology

Re: How would I set up an experiment to test for lead in candle soot?

Date: Mon Jan 15 16:17:22 2001
Posted By: Bob Weeks, Staff, Environmental Science, NMED DOE Oversight Bureau
Area of science: Environment & Ecology
ID: 978552224.En

One approach would be to put an inverted pyrex funnel above the candle and
to then vent the smoke through a piece of Tygon tubing attached to the
funnel stuck into a glass of deionized or distilled water in which some
sodium sulfide had been dissolved. The idea would be to have the soot from
the candle ultimately reach the aqueous sodium sulfide solution. If the
soot contained lead, it should react with the sulfide ion and form a
precipitate which would then make the solution turbid.

Another approach would simply be to hold a glass plate above the burning
candle such that soot deposits on the glass. The soot could then be brushed
into a test tube containing a dilute nitric acid solution. The nitric acid
would assure that all of the Pb would go into solution.  Then put a drop or
two of this solution on one of the test strips. If the drop darkens the
test strip, this is indicative of the presence of Pb as shown by the
presence of the dark PbS (lead sulfide).

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