Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/697

Rh MANUFACTURE.] WOOL 657 is not sufficient for the ordinary purposes of the manu facturer. The scouring process is thus the first link in the long chain of manufacturing processes through which wool passes. On the careful and complete manner in which scouring is effected much depends. The qualities of the fibre may be seriously injured by injudicious treat ment, while, if the wool is imperfectly cleansed, it will take on dye colours unevenly, and all the subsequent manufacturing operations will be more or less unsatisfac tory. The water used should be soft and pure, both to save soap and still more because the insoluble lime soap formed in dissolving soap in hard water is deposited on the woollen fibres and becomes so entangled that its removal is a matter of extreme difficulty. Wool washed with hard water is always harsh to the touch, and takes on dye colours but unevenly, owing to the interference of unremoved lime soap. In former times stale urine was a favourite medium in which to scour wool ; but that is now disused, and a specially prepared potash soap is the detergent principally relied on. Excess of alkali has to be guarded against, since uncombined caustic acts ener getically on the wool fibre, and is indeed a solvent of it. On this account a soap solution of too great strength leaves the wool harsh and brittle, and the same detrimental result arises when the soapy solution is applied too hot. In former days, when the method of hand-scouring pre vailed, the wool to be washed was placed with hot soap- sud in a large scouring &quot;bowl&quot; or vat, and two men with long poles kept stirring it gently about till the detergent loosened and separated the dirt and dissolved the grease. The wool was then lifted out and drained, after which it was rinsed in a current of clean water to remove the &quot;scour,&quot; and then dried. These operations are now per formed by mechanical agencies; and, to save soap, it is the practice to first steep the wool in steepers, tubs having a perforated false bottom in which steam is blown through the wool steeped in pure water. The process removes much mechanically mixed dirt, and softens the other impurities, expanding the fibres themselves, and thus rendering the scouring operation easier and more expedi tious. In machine scouring the object aimed at is to bring all the wool equally under the influence of the soapy solution, and to prevent it from matting into lumps in its progress through the washing bowls. Usually the wool passes through two sets of bowls, the soap solution being stronger in the first set. The wool is fed into one extre mity of the bowl, which is an oblong vat, by an endless apron from which it passes to an immersed plate which sinks it into the hot soapy solution, where the whole is thoroughly soaked. It is then carried to the opposite end of the bowl, either by a series of forks or rakes with reciprocating motion, or by sets of iron prongs fixed at a uniform distance on a frame to which recipro cating action is communicated by eccentric mounting. These carry the wool forward by gentle progression, so as not to ball it, till at the upper end it is caught and squeezed between rollers to wring out part of the water from the fibres, and then passed on for further drying. The more gently and uniformly the drying can be effected the better is the result attained, and over-drying of wool has to be specially guarded against. By some manufacturers the wool from the squeezing rollers is whizzed in a hydro-extractor, which drives out so much of the moisture that the further drying is easily effected. The commonest way, however, of drying is to spread the wool as uniformly as possible over a framework of wire netting, under which are a range of steam-heated pipes, the sides being enclosed in a framing of wood. A fan blast blows air over these hot pipes, and the heated air passes up and is forced through the layer of wool which rests on the netting. Unless the wool is spread with j great evenness it gets unequally dried, and at points where the hot air escapes freely it may be much over-dried. A more rapid and uniform result is obtained by the use of Petrie s wool drier, which consists of a close chamber divided into five horizontal compartments, the floors of which consist of alternate fixed and movable bars. Under the chamber are a tubular heating apparatus and a fan by which a powerful current of heated air is blown up the side of the chamber, and through all the shelves or compartments successively, passing in the path over which the wool slowly travels. The wool is entered by con tinuous feed at one side of the chamber; the strength of the blast carries it up and deposits it on the upper shelf, and by the action of the movable bars, which are worked by cranks, it is carried forward to the opposite end, whence it drops to the next lower shelf, and so on it travels till at the extremity of the lower shelf it passes out by the delivery lattice well and equally dried. Moore s drier is a simpler and less expensive form of drying apparatus, intermittent in its action. It consists of a case enclosed except as regards the top, where there are openings to allow the escape of moist air. It contains two tiers of steam-heated pipes, and directly over the top of each tier there is a row of iron rollers of small diameter set close together. At one end of the machine is a door for feeding wool into it, and at the opposite extremity is a spiked drum geared to rotate at a high speed. A fixed quantity of wool is fed into the machine at one time and placed on the lower series of rollers. These in their rotation carry the wool forward exposed to the heat of the pipes both above and below, till it reaches the drum, which, revolving rapidly, lifts it to the higher range of rollers. Over these the wool is carried back, till at the other end it again falls to the lower range, and so it circulates through the machine till the drying is completed. To withdraw the dried wool it is only necessary to raise the outlet door over the revolving drum, when it throws out the contents of the machine as fast as the wool comes within its range. The dried wool, notwithstanding the several manipula- Teazing. tions to which it has been subjected, is still in the condition of matted locks, which have to be opened up and the whole material brought into a uniformly free and loose condition. This is effected in the Willey or teazing machine, which consists of a large drum and three small cylinders mounted in an enclosed frame. The drum is armed with ranges of powerful hooked teeth or spikes, and is geared to rotate with great rapidity, making about 500 revolutions per minute. The smaller cylinders, called workers, are also provided with strong spikes ; they are mounted over the drum and revolve more slowly in a direction contrary to the drum, the spikes of which just clear those of the workers. The wool is fed into the drum, which carries it round with great velocity; but, as it passes on, the locks are caught by the spikes of the workers, and in the contest for possessing the wool the matted locks are torn asunder till the whole wool is delivered in a light, free, and disentangled condition. For certain classes of dirty wool, notably such as that Burring, which comes from Buenos Ayres, still another preparing operation is essential at this stage that is, the removal of burrs or small persistently adherent seeds and other fragments of vegetable matter which remain in the wool. Two methods of effecting this one chemical, the other mechanical may be pursued. The chemical treatment consists in steeping the wool in a dilute solution of sulphuric acid, draining off the dilute acid by means of the hydro-extractor, and then immediately exposing the wool to further rapid drying in a heat of about 250 F. The acid leaves the wool itself uninjured, but is retained XXI V. 83