It ought, however, to be known, that _boiling_ wool _for a long time_ in any alkaline liquors, or a liquor made of soap, tends greatly to the decomposition of the cloth; indeed long boiling in any strong alkaline ley converts wool into a kind of soap, and, hence, it is easy to see why such processes injure wool or cloths made with it. The preceding observations apply to the alkalies in a _caustic_ state, or in the state of _carbonate_, not when they are neutralized by powerful acids: for wool, when fit to receive the dyes, and if it is designed to be dyed _yellow_, should boil two hours with one-twelfth or one-tenth of its weight, of sulphate of alum (common alum) observing proper precautions, and the use of a sufficient quantity of prepared weld plant boiled, &c.: or of quercitron bark, as will be shown in the processes of the different yellows. If it were yarn, and the threads cut in two, it would be found dyed throughout, and of a body and richness in proportion to the correct application of the various ingredients, and with due regard to time, weight, measure, &c. In the process just mentioned, we may observe, that the quantity of alum and of the weld plant used will be found very considerable: from one twelfth to a fourth of alum, and, according to the French method, four or five times more weld than the quantity of the wool. When a process of dyeing has been scientifically conducted, the wool will take so much of the alum that the bath will hardly taste of it; and afterwards take the colour of the dye bath out of it; so that the remaining liquor put into a glass will be nearly like water. _The action of alum and tartar upon wool._ From the experiments of Dr. URE, (_Notes to Berthollet_, vol. ii. p. 323.) it appears that alum has the property of increasing the solubility of cream of tartar; that as, in using alum and tartar, the wool is impregnated with alum and a large quantity of tartaric acid, these two salts should never be employed together, except when the colour is susceptible of being heightened and rendered brighter by acids, as is the case with cochineal, madder, and kermes. On the contrary, alum should never be employed for wools intended to be dyed with woad, or Brazil wood, the colour of which is easily destroyed or altered by acids. To conclude these preliminary observations, wool has a strong and powerful affinity for _all_ dyeing materials; and, therefore, the processes for dyeing wool are, in general, by no means so complicated as those for dyeing _cotton_, _silk, &c._; although some colours, even to these, are readily, and without a complication of processes, imparted. _A pastil, or woad vat for_ BLUE.