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vantages; and besides, where this quality is desired, analmost equal glossiness may be obtained by means of gum.

I tried likewise to prepare an ink, in which the colour-ing parts should be secured by a resinous varnish. Hereno water could be used, the dissolution of the resin re-quiring strong spirit of wine j and as this spirit does notdissolve the vitriol of iron, another preparation of themetal became necessary. Iron filings were digested inspirit of salt, with a moderate heat, till the acid woulddissolve no more; and the solution being set to evaporatetill it became thick, it was in this state diluted with rec-tified spirit of wine : this preparation is the tinBura martisin spiritusalts of the apothecaries. I made a strong tinctureof galls in spirit of wine, and dissolved in it as muchmastich as it would take up : with this solution pouredoff clear, I mixed different proportions of the tincture ofiron, and obtained bluish-black liquors, of a pretty goodblackness when written with, and sufficiently durable,but unfit for the common purposes of ink, on account oftheir spreading and sinking in the paper, and growingclotty in-the pen. Part of the mastich seemed to be pre-cipitated on mixture with the tincture of iron, as resinousbodies generally are with acids; whereas gums dissolvein acids without precipitation.

Instead of the preparation of iron, called green vitriol,some have recommended the blue vitriol of copper, andethers the white vitriol of zinc. The white vitriohthough its principal metallic matter be zinc, generallycontains also no inconsiderable quantity of iron, and invirtue of this iron it strikes a black with galls. Manyblue vitriols also have a mixture of iron with the copper,and in this cafe they may in like manner strike a blackwith astringents. To common green-vitriol I added dis*ferent proportions of the pure vitriols both of zinc and

copper: