The opinion, therefore, of teas deriving their green colour from being dried upon copper being founded on a misrepresentation of the manner in which they are really prepared, a few observations upon the subject are indispensibly necessary. For those who have always understood that the detrimental qualities of foreign teas were the consequence of their being dried upon copper, may perhaps imagine they cannot 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 dangerous. And in a country, like Great Britain, Holland, and other places, where a cloudy atmosphere, caused