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proportions they are used, produce no other than brownsof different shades : I have often been surprised, that withthese capital materials of the black dye I never couldobtain any true blackness in white cloth, and attributedthe failure to some unheeded mismanagement in the pro-cess, till I found it to be a known fact among the dyers.Logwood is the material which adds blackness to thevitriol and gall brown ; and this black dye, though not ofthe most durable kind, is the most common. On bluecloth, a good black may be dyed by vitriol and galls alone;but even here, an addition of logwood contributes not alittle to . improve the colour.

8. The addition of verdegris, which deepens the colourof the inky liquor, is found also to deepen the dye oncloth; and this improved blackness, very perishable inthe ink applied on paper, appears in cloth to be moredurable, though not entirely so much as could be wished.The effect of the verdegris seems to proceed from itsaction on the logwood : for with galls, and with greenvitriol, separately, it produced no tendency to black-ness ; but with decoction of logwood it struck immediatelya deep black, which when diluted appeared of a fine blue.This experiment reconciles two observations I have latelymet with, one by Mr. Scheffer in the Swedish Trans-actions, the other by Mr. Hoffmann in a German treatiseof œconomical chemistry, &c. the former of whom re-lates that logwood with verdegris gives a blue dye, andthe latter that it gives a black. Blue is the proper colourof the mixture, and the black is a concentration of theblue. Part of the colouring matter of the mixture con-cretes very speedily into sensible particles, so as to looklike a black powder diffused through the liquor : theliquor is found to pass blue through a filter, and theblack matter, which remains on the filter, appears like-wise