185. In the raw state, wool is covered by a sort of unctuous matter called yolk, or suint, which preserves it from the attacks of moths, and, on that account, ought not to be prematurely removed. This substance has been examined by Vauquelin, and appears to be a kind of animal soap, hating potash for its basis, together with a quantity of fatty matter, and a portion of lime in combination with the carbonic, acetic, and muriatic acids. The wool of healthy sheep is always more abun dantly covered with yolk than that of the sickly and diseased.
186. Before wool is submitted to the operation of dyeing, the yolk is 'moved by scouring or maceration for about a quarter of an hour in water, mixed with a fourth part of stale urine, and heated so as the hand can just bear the temperature. After being duly stir red in this mixture, it is taken out and drained ; it is then carried to a stream of running water, and moved about till the greasy matter appears to be completely separated, and ceases to render the water turbid. M. Vauquelin recommends, that the wool, after being cleansed as effectually as possible with pure water, should be soaked for a few hours in a tepid solution of soap, one pound of soap being employed for every twenty pounds of wool to he scoured. Dl. Roard is of opinion that one pound of Flanders soap, employed in this manner, is sufficient for thirty pounds of wool ; he recommends, however, that the water should be heated to 60° of Reaumur, (167' of Fahrenheit.) He affirms that wool which has been spun in the yolk, and scoured afterwards, is much whiter than if scoured before being spun. Whatever method is adopted, the scouring should be performed with great care, as the wool is rendered, by that operation, much fitter for receiving the dye.
187. The wool is dyed in the fleece, or before being spun, chiefly when it is to be manufactured into cloths of mixed colours, and it is dyed after being spun when it is intended for tapestry. But it is most commonly dyed af ter it has been manufactured into cloth. When wool is dyed in the fleece, its filaments being separate, are in a situation for absorbing a greater proportion of colouring matters than when it is spun, and still more than when it is in the form of cloth ; but different woollen stuffs vary considerably in this respect, according to their fine ness and closeness of texture. These circumstances taken into consideration with the different qualities of dyeing ingredients, prevent us from relying with implicit confidence on the processes usually recommended.
188. After wool has been spun and wove, it is sub jected to the operations of felting and fulling. Accord ing to the observations of M. Monge, the fibres of wool consist either of a great number of small lamina over lapping one another from the root to the extremity, or of a series of annular concretions, like the horns of ani mals, gradually decreasing in diameter towards the point. From this structure of the woolly fibre, if a hair be held with one hand by the root, and drawn between the thumb and finger of the other hand, scarcely any friction or re sistance is perceived ; but if it be drawn in like manner, in a contrary direction, a tremulous motion is distinctly felt, accompanied with a sensible grating noise. By this conformation of the fibre, a hair when it is pressed must suffer greater resistance, when it slides in the direction of the point, than in that of the root ; and to obviate the inconvenience which this would occasion in spinning, wool is covered with some unctuous matter, which in some measure smooths its asperities, and thus facilitates that operation. After the wool is manufactured, the oil being no longer useful, is removed both for the sake of cleanliness, and to enable the stuff to absorb more effec tually the dye. The cloth is therefore taken to the full ing mill, where it is beaten with large beetles, in a trough of water, containing diffused through it a quan tity of fullers earth. The earthy matter uniting with the oil, forms a kind of soap, which is carried off by the constant action of the machinery, and the effusion of fresh portions of water. See WooL.
189. Silk is of animal origin, and consists of the fine threads with which the bombyx marl, a moth belonging to Limmus's third order of insects, envelopes itself be fore it emerges in the perfect state. Silk is naturally co vered with a gummy or glutinous substance, to which it owes its stiffness and elasticity ; it is also frequently tinged with a yellowish colouring matter. The purposes for which silk is usually employed, require that it should be freed from both these matters ; and this is commonly done by means of soap. Besides the gummy and co louring matters, there is also, according to Roard, a sub stance to be removed, which has a considerable resem blance to wax. He states, that the zummy matter.