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SECT. IV.

Black produced by mixture.

I. Black from Iron.

F ROM infusions of certain vegetables, mixed withgreen vitriol, is produced a deep black liquor, ofmost extensive use for dying and staining black. To wool-len and silk it gives a permanent cblour, although fromlinen, and other vegetable bodies, its blackness is dis-charged by washing.

The substances chiefly employed for producing this co-lour with vitriol, are the excrescences of the oak free,called galls; of which there are two principal kind§, onesaid to be brought from the Levant, and the other fromsome of the southern parts of Europe, particularly Sicilyand Romania. The former, called by authors Aleppogalls, and in the scops of our dry-salters blue galls, aregenerally of a bluish colour, or of a greyish or blackishverging to blueness, unequal and warty on the surface,hard to break, and of a close compact texture : the others,commonly called white galls, are of a pale brownish orwhitish colour, smooth, round, easily broken, less compact,and of a much larger size. The two forts differ in strength,but in other respects they appear to be of the same quality.The Aleppo or blue galls are the strongest : two parts ofthese are reckoned by the workmen to be equivalent tothree of the white; and such comparisons, as I have madeof the two, incline me to think, that the difference in theirstrength is rather greater than this proportion.

These excrescences appear to proceed from the juicesof the oak tree issuing out through small wounds made bycertain insects; which insects not being found in this Cli-mate, no galls are here produced though other kinds of

excrescences