Woad Vat.—These vats are extensively employed at Louviers, and in the manufactories of the north of France. The bath is prepared in the same manner as in the foregoing case; the finely cut root is introduced into the copper along with 2 lbs. of pounded indigo, 9 lbs. of madder, and 15½ lbs. of slaked lime. The liquor is, after the necessary ebullition, poured upon the woad. This substance contains but a very small quantity of coloring principle; we must, therefore, add some indigo when preparing the vat, so as to indicate the precise instant when the mixture arrives at the point of fermentation so necessary for imparting hydrogen to the coloring principle, and for rendering it soluble. We must also use a larger quantity of lime, since the woad contains no ammonia resulting from previous decomposition, such as we find to be the case with the pastel of the south. When the vat is in a suitable state of fermentation, a rusty color becomes manifest, in addition to the signs already described in speaking of the pastel vat; besides the ammoniacal odor, the bath always retains the peculiar smell of the woad. The pounded indigo is now added, and we proceed, in the manner already detailed, to reduce it to a state of solution fit for dyeing. The vats prepared by means of pastel have greater durability than those made with the woad; but it is thought that the colors given by the latter are more brilliant than those obtained from the former dye. Modified Pastel Vat.—This vat is about 7 feet in depth, and 6½ feet in diameter. It is made of copper, and heated by steam. The lid is composed of three segments, each of which is formed of two planks, about an inch thick, and strongly secured together by bolts. The beating is performed in the usual way, with sticks before the first dipping, after having moistened the cloth in tepid water. This operation is not subsequently repeated.