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wise merely blue, when spread thin on paper, or dilutedwith white powders.

9. Instead of the verdegris, I tried a cheaper preparationof copper, blue vitriol. This had somewhat of a likeeffect, but in a less degree : the colour on mixture wasless black, and the concretion of the colouring parts lessremarkable : the black or bluish-black matter being sepa-rated by filtration, the liquor proved not at all blue, butpurplish or reddish, much like a decoction of logwoodby itself; it soon turned to a blue colour when dropt onpaper and exposed to the air, but both the blue and theblack were greatly more perishable than those producedby verdegris.

10. Some have preferred vitriols impregnated with alittle copper, as that of Dantzick, to the more purelyfertugineous English vitriol ; not indeed suspecting thatthe copper would add any thing to the colour, as in theforegoing experiments ; but from an opinion of its ren-dering the vitriol more penetrating or corrosive, so as toenable the colouring matter to sink better into the subject.With regard to its adding colour, if the vitriol of copperwas even as effectual in this intention as verdegris, which itis very far from being, yet the very small quantity, containedin the vitriols Recommended, could be of no material ad-vantage ; and as to the penetration, I believe it will beadmitted, that vitriol of iron without any copper is pene-trating and corrosive rather more than enough. TheDantzick vitriol appears however to have one advantage,not depending on its coppery part, but on the mannerof its preparation : greatest part of the English vitriol, byhasty crystallization, is run into large irregular masses,abounding with loose ochery matter and with waterymoisture, if not with foreign substances of another kind;while the Dantzick, more slowly crystallized, is more

pure,