Re: The rusting of iron

From: Bevan Price (bevan$£$DELETETHESE$£%%price_at_freeuk.com)
Date: 06/01/04 

Date: Tue, 1 Jun 2004 18:29:03 +0100

"Mohammed Farooq" <farooq_w@hotmail.com> wrote in message news:66756669.0405311951.6d7f77f0@posting.google.com...
> [Farooq wrote]
> >A discussion was started on "odor of metals" in sci.chem on
> >2003-03-28, and most of the people attributed the characteristic
> smell
> >of each metal due to its oxide. Clean copper does not smell but an
> old
> >copper would, so is the case with iron ( characteristic smell of
> >rust). An argument in the support of metal-oxide hypothesis is that
> >noble metals (I can say of pure gold and silver) do not have a
> >(detectable) smell.
>
> [Steve Turner ]
> >I remember the thread. But I don't agree with the assertion that the
> >smell is caused by oxide. Most metal oxides are very nonvolatile
> >(osmium being a notable exception). The nose cannot detect that which
> >is not in the air to begin with.
>
> Indeed the non-volatility of metal oxides is a valid point, but we
> still smell something "metallic" in our hands after _touching_ an old
> copper wire and an old rusted iron nail. Do you think that chemicals
> from our skin (as someone earlier suggested in that thread) form
> volatile compounds (N-, S-) with the metal which can be detected by
> our nose? Though I personally do not thnk that.
>
> Coming to non-metals, which do not form oxides readliy or are so
> unreactive that one can assume they would not react with something
> else in the air, do have characteristic odor, such as that of sulfur,
> or some metalloids like selenium and tellerium. What is our nose
> bascially detecting sulfur, or selenium in the air or their compounds?

I did not see the original thread, but many commercial-grade metals contain traces of non-metallic impurities such as C,
N, S, P, etc. Traces of these at the metal surface may be able to react with moisture in the air, or on the skin, to
produce volatile compounds with distinct odours. For example, you only need a very small quantity of H2S or PH3 for it
to be detected by its smell.

Bevan

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