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materials, and consequently be less weakened, than if itwas dyed directly from white to black. But there isanother more important use of it, the blue being essentialto the production of the black dye; for without either a ,blue ground, or a blue superadded to the vitriol and galls,no other than brown dyes are obtained. There are means,(fee hereafter N°. 7.) of introducing this necessary blue-ness along with the vitriol and astringents ; but the colourproves more perishable than when dyed upon a blueground of indigo or woad.

4. The dyers commonly leave some blue marks at theends of the cloth, by fixing pieces of lead on them, bywhich they are secured from the action of the black liquor,to shew that the piece has been regularly dyed on a blueground, and consequently that the colour may be expectedto be durable. This may be discovered, with greatercertainty, by steeping a small bit of the black cloth, fora day or two, in water acidulated with a little oil ofvitriol; or more expeditioully, by boiling it about a quar-ter of an hour, in a solution of alum and tartar, made inthe proportion of an ounce of each of the salts to a pintof water. Great part of the black matter being destroyedor dissolved by the saline liquors, the cloth will remainof a bluish black colour if it has had a previous blueground; but if it has been dyed directly from white, itwill now look of a muddy reddish brown. The solutionof alum and tartar is the essay liquor for black cloths,directed in the new French regulations, which weredrawn up from the experiments of Dufay, and publishedat the end of Hellots Art de teindre «

5. Stusss, whose price will not admit of the blue dye,are said, by the French and German writers, to begrounded with a deep brown, by boiling them with wal-nut peels, or walnut-tree roots. This practice, as I am

informed,