I 379 J

manner retain the redundant impregnation of the galls,and strike a blackness with fresh vitriolso that by try-ing, till such proportions of the two should be sound, asthat the liquor, aster the precipitation, should produce noblackness with a fresh addition of either ingredient, theproportions requisite for the exact saturation might bediscovered. <.

Many trials were accordingly made on this principle.When the quantity of galls was several times greater thanthat of the vitriol, an addition of more vitriol to the liquorafter settling produced afresh blackness; and when the vi-triol greatly prevailed, an addition of galls had the like effect.But there were several intermediate mixtures, with pro-portions considerably different from one another, in whichiio blackness could be perceived to arise from the additionof one or the other ingredient. By taking a medium be-tween the quantities, in those trials where one or the otherdid produce a sensible colour, it was reckoned that aboutequal parts of the two were the mean proportions, whichcould receive no additional blackness from a further in-crease of either. In these and all the other experimentsmade with galls, the Aleppo or blue galls were the fortemployed; and care was taken, by boiling or long infu-sion, to get out as much of their virtue as can be expectedto be done in practice.

Different infusions of the galls and vitriol, in a moreand less dilute state, were tried next on paper. Here itwas found, that the proportions, which gave the greatestblackness, were not those, whose colours were the mostdurable, though in both respects there were considerablelatitudes. Equal parts of the two, the quantities whichthe foregoing Way of trial seemed to point out for thehestz.gave an ink of good blackness at first; but on keep-ing for a few weeks, and in a few days when exposed to

D d d the