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position of the dying ink if it may be lo called; mixtures,which prove too perishable when applied iuperficially onpaper, being of sufficient durability when introduced intowool or woollen cloth; and mixtures, which make a goodblack ink on paper, making only a brown in the dyersbusiness.

2. Cloth is generally supposed to be weakened by theblack dye, more than by any other; on account of the cor-rosive quality of the vitriol, which is increased by the heatmade use for making it thoroughly penetrate the subject:though the vitriol of iron is much less corrosive than thesolutions of the metal made in the nitrous and marineacids, it is reckoned much more so than the alum andtartar employed in most of the other dyes. The finer theblack, the more it is thought to weaken the cloth; inso-much that some writers look upon the beauty of the co-lour, and its durability or innocence to the cloth, as beingincompatible with one another, and hence think it ad-visable to abate a little in both points, and to be satisfiedwith a colour of moderate fineness that the cloth may bemoderately lasting. A German writer on dying, distin-guished by the approbation of the celebrated Stahl, placesthis affair in a somewhat different light. He observes thatthe vitriol proves corrosive only so far as it is not saturatedwith the galls, and that by using a proper quantity of galls,it will be mortified, so as to be incapable of doing anyinjury to the cloth: to determine the quantity sufficientfor this complete saturation, he directs a decoction of thegalls, and a solution of the vitriol, to be mixed together indifferent proportions, and dropt upon white paper, the li-quors being made very dilute that their colours may be thebetter judged of: the proportions, which give the deepestblack colour, are those which ought to be followed bythe dyer, and by which, according to him, the vitriol is

made