Those who frequent the sea-coast are not long in discovering that their
best dyed black hats become of a rusty brown; and similar effects are
produced on some other colours. The brown is, in fact, _rust_. Most, if
not all, the usual black colours have iron for a basis, the black oxide
of which is developed by galls, logwood, or other substances containing
gallic acid. Now the sea-air contains a proportion of the muriates over
which it is wafted; and these coming in contact with any thing dyed
black, part with their hydrochloric (_muriatic_) acid, and form brown
hydrochlorate of iron, or contribute to form the brown or red oxide,
called rust. The gallic acid, indeed, from its superior affinity, has
the strongest hold of the iron; but the incessant action of the sea-air,
loaded with muriates, partially overcomes this, in the same way as any
acid, even of inferior affinity to the gallic, when put upon black
stuff, will turn it brown.--_Ibid._
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