Among the different authors of any consequence that have written on the culture, preparation, and virtues of foreign teas, may be ranked Kampfer, Postlethwaite, Dr. Cunningham, Priestley, Lemery, Franchus, Meister, and Sigesbeck; as the limits of this Treatise will not permit a detail of observations from the whole of these writers, remarks can only be selected from the most principal of them. Most of the above, and many other, authors agree that the leaves are spread upon iron plates, and thus dried with several little furnaces contained in one room. This mode of preparation must greatly tend to deprive the shrub of its native juices, and to contract a rust from the iron on which it is dried. This may probably be the cause of vitriol turning tea into an inky blackness. We therefore do not think with Boerhaave, that the preparers employ green vitriol for improving the colour of the finer green teas. It may however be concluded, from the colour of bohea, souchong, and such as are called black teas, that they may be thus tinctured, by the means of vitriol, after they have been dried upon the iron plates in the furnace room; and this may likewise particularly cause that astringent quality which is more experienced in all the black than any of the green teas. According to Sigesbeck, the colours of these teas are artificial; so that if these pernicious arts are used even to give the tea a particular colour, there is no difficulty in ascribing the cause of their injurious effects.