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tains a matter similar to the galls which are producedfrom it. Possibly by some preparation of the oak-dust,it might be brought nearer to the nature of galls : doesnot its difference- from galls depend on fomfe particularjuice, more soluble than the direct astringent wattes, andseparable by flight infusion in cold water ?

VII. Black dye from a combination of colours.

In the first article of this section it has been lhewn,that the madder dye, 1'equired by the French regulationsto be applied upon blue cloth as a ground for black, israther injurious to the colour than of any real advantage.In the experiments which the determination of that pointrequired, a somewhat unexpected phenomenon occurred,an account of which was reserved for this place. Apiece of deep blue cloth was boiled in water with alumand tartar, as customary for preparing cloth to receive themadder dye. The cloth being taken out and squeezeda little, some powdered madder was boiled in water, insuch quantity as to communicate a dark red colour to theliquor. The cloth, still moist, was put into this decoction,and a boiling heat continued about half an hour. Beingthen taken out and wassied with soap, it looked of a verydark colour, such as any person, would call a black, thoughnot a sine black. Thus we have a kind of black dye,very durable, without any vitriol or other preparation ofiron, from a combination of the blue dye with the mad-der red..

This effect of madder upon blue cloth is well knownto the dyers, among whom the colour hence produced iscalled madder-black. Our black cloths for home con-sumption are all dyed with vitriol and astringents, eitheren a ground of woad, which makes the true black, orwith an addition of logwood only, in which cafe the.

colour