Page:The New International Encyclopædia 1st ed. v. 18.djvu/209

* SILK. 167 SILK. ing the Civil War Paterson became, anil has siuce remained, the chief seat of silk manufac- ture in the United States. riiocESSES OF Mani^facture. Although raw silk, unlike other textile fibres, is a cuutinuous thread, and therefore requires no spinning, yet its preparation for the loom includes many dis- tinct operations. After the cocoons that are to be saved for breeding purposes are set aside, those to be used for their silk are submitted to some treatment that will kill the chrysalis with- out injury to the cocoon, just at the time when the insect has finished spinning and is ready to force its way through its covering. Several methods have been adopted for accomplishing this end. The chrvsalis may be destroyed in a hot oven, or by placing it in the hot sun for several days under glass, or by a steam-bath. The last-named method was invented by Profes- sor Castrogivanni, of Turin. The cocoons are placed under an iron receiver, where steam is ap- plied at a uniform temperature of 212° F. One objection to this process is that the pupa sometimes bursts, soiling the silk. It is said that the Chinese reel ofl' the silks from the cocoon while the silkworm is still alive. Reeling. In order to be able to remove the silk from the cocoon, the latter is soaked in warm water, which loosens the gummy substance bind- ing the filaments together. As a single fibre has not sufficient tenacity, from four to eighteen fila- ments, according to the quality, are taken, and two threads formed by passing them through per- forated metal or porcelain guides. The threads are erosseil or twisted together at a given point, and again separated and passed through a second pair of guides, the temporary twisting or crossiiig causing the agglutination of the individual fibres of each thread. The thread is then passed through a pair of distributing guides onto the reel. Great care and skill are required in reel- ing silk from the cocoons, to keep the thread of uniform thickness. The threads of different cocoons are not of uniform length, and that from the inner part of the cocoon is finer than the out- side, so the filament from another cocoon must now and then be added to keep the thread even. The common reeling machine is a simple device consisting of a reel 60 to 90 inches in diameter, adjusted in a frame which contains the guides, the water basin, and means for keeping the water warm. Reeled silk is the raw material of the silk manufacturer, called raw silk. It is shijiped by the silk-growers in hanks of various sizes, packed in bundles or bales. Stlk Conditioning. One of the most striking physical eliaraetcristics of raw silk is its avidity for moisture; it will readily absorb 30 per cent, of its weight in moisture without the fact being perceptible. In order, therefore, to determine the amount, of normal silk in a given bulk, the raw silk is tested in an apparatus called a des- iccator. This is done by first weighing a sample, then drying it and noting the loss of weight. To the thoroughly dried silk an allowance of 11 per cent, is added and the result taken as normal weight. In the great centres of silk manufacture the testing is required by buyers and is done by special houses called silk-conditioning estab- lishments. Throwing. The process of preparing the reeled silk for the loom is technically called tlirowing. The first step is to transfer the silk from the skeins to bobbins. The skeins, inclosed in a light cotton bag, are soake<l for several hours in soapy water at 110° F. The.v are then dried in a hydro-extractor and stretched upon swifts, which are skeleton reels so adjusted that they will hold the skeins tightly. Thence they are woiuul onto bobbins. The silk is next cleaned by passing it from one bobbin to another through the cleaner, which consists of two parallel plates so adjusted that there is just room for the thread to pass through. Adhering dirt or an imper- fection in the thread at once holds the thread and at the same time arrests the motion of the spindle until the operator removes the cause. The best Italian silk does not require this process of cleaning, but for Chinese silk it is always necessary. Doubling and Twisting is the next process performed, and the manner in which it is done gives the name to the three difl'erent silk threads. (1) Single silk is not doubled or twisted at all, but is woven direct from the clean- ing process. Cloth produced in this way pos- sesses a softness and brilliancy not obtainable in that made from twisted silk. Pongee is a famil- iar fabric made from singles. (2) Tram silk is made b.y twisting two or more single threads which are then doubled and slightly twisted. It is used for the woof thread in weaving. (3) Or- ganzine silk is made by the union of two or more single threads, twisted separately in the same direction, which are doubled and then re-twisted in the opposite direction. It is used chiefly for warp threads. Scouring is the process applied to thrown silk to remove more or less of the glue adhering to the silk thread, so it will have a greater lustre and may be able to take a better color in dyeing. According to the amount of gum removed in scouring, silk is known as 'boiled, in which from 24 to 30 per cent, is removed ; souple, in which onl.v from 5 to 8 per cent, is removed ; ecru, in which not more than 5 per cent, is removed. The scouring is performed in soapsuds. The silk is now ready to be dyed, although for white or pale shades it must first be bleached in sulphur fumes. Shaking, Glossing, and Lit.string are sup- plementary processes for which special machinery has been devised, designed to develop the lustre of the silk. Loading or Weighting of Silk was, in the beginning, an attempt on the part of silk dyers to make u]i for the loss offiveight, often amounting to one-fourth, incurred during the process of scouring, by the use of certain chemicals which, combining with the silk, took up the dye. For a time weavers were satisfied if the dyeing pro- cess was so conducted that there was no loss of weight. But the art of imparting factitious weight to silk was soon developed tn a ruinous extent. Sugar and glucose were at first the favorite agents of sophistication, but were soon abandoned for more effective materials. In black silks the extreme weighting was first practiced, a pound of silk being treated so as to weigh 100 ounces. The discovery of the use of salts of tin, however, has made it possible to weight the white and colored silks as heavily as black. By this process the dnrabilit.y of the silken fabric, once its most prominent characteristic, is en- tirely lost.