be so
pernicious if they were dried upon iron; but this opinion cannot be
entertained by any persons who have the least knowledge of the manner
in which the vegetable acid will corrode iron. Those who are acquainted
with culinary processes must know in what manner the acid of onions
will operate upon any steel instrument; it corrodes a knife so as to
turn the onions black with the particles eaten away from the edge and
the face of the blade. To avoid this unwholsome and unseemly
inconvenience, a wooden instrument is generally used in all instances
where onions form a part of the cookery appendages. It is consequently
evident, that although iron utensils are now greatly used instead of
copper, yet many injurious effects may happen from their being liable
to be corroded by the acid of several vegetables. And if the nitrous
acid of the air will corrode iron so as to cause rust, when it will not
produce the proportionate effect upon copper, it is a demonstration
that iron is the most liable to such a corruption. The corrosions of
copper are undoubtedly pernicious; but the damage that tea would derive
from its being dried upon sheets of this metal would not operate so
injuriously to those who drink it as it does now by lying dried upon
iron. For the latter bring more liable to the power of the mineral,
vegetable, or animal acid, must impart more particles of its reduced
calax to the tea than copper would. And, in order to shew how
susceptible of corrosion iron is, the following instance is farther
adduced: in Ireland, where some persons practise the art of tanning
leather with fern, which possesses a very strong acid, particular care
is taken to avoid using any iron vessels in the tannage, lest the
colour of the leather should be blackened by the corroding particle of
the metal. As it is the peculiar property of iron or steely particles,
even in their most perfect state, to operate as too great an astringent
for an aliment that is taken twice a day constantly, tea, when dried
upon it, must be rendered proportionably pernicious. But admitting that
the popular opinion of their being dried upon copper was just, the teas
must be rendered proportionably injurious to the quantity of copperas
or crude vitriol they imbibe from their acidity corroding the metal.
Preparations of steel, that are, in many instances, considered as most
salutary, yet in all pulmonary disorders the most eminent physicians
have deemed them exceedingly dange