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To reassure those who wonder how doctors dare administer nitric oxide
to babies if it ‘quickly combines with oxygen to form nitrogen dioxide (‘The
body’s vital poison’, 13 March) may I point out that this is true only
for high concentrations. The kinetics of the reaction are such that the
very dilute gas generated biologically or used medically does not oxidise
significantly. At Barts we measured its concentration in London air daily
and far from being ‘highly reactive’ it was so inert that we could find
no direct chemical method for doing so. It first had to be oxidised, and
the devil’s own job it was. We finally used a mixture of strong sulphuric
acid and permanganate, which turned everything dark brown and tended to
explode if allowed to warm up. Nowadays of course it is all done electronically,
in a ‘black box’ costing about £10 000.

Tom Nash Sherborne, Dorset