SILK.
Silk is by far the strongest of the textile fabrics, being nearly three times as strong as flax; it consists of the filaments spun by the silk-worm, Phalœna Bombyx Anori. These filaments are always double, proceeding from two holes in the head of the worm, and are united by a sort of varnish which is moist and clammy when the threads proceed from the insect, and causes them to adhere together. The silk-worm in spinning, moves the head backwards and forwards, attaching the threads on alternate sides and all around till it is completely covered in with a ball of silk; in this state it is called a “coccoon.” The silk-worm, like others of its class, undergoes four changes or metamorphoses—the Egg, the Grub or Worm, the Chrysalis, and the Imago or perfect insect, which, in this case, is a moth. The worm spins the coccoon to defend itself from injury and cold, but man, taking advantage of the useful qualities possessed by these fine filaments, spins them into his most gorgeous apparel. The coccoons are unwound by placing them in a basin of warm water, which dissolves the varnish, and they are then slowly wound off; formerly this was done by hand, but now machinery is chiefly employed which winds off the silk from a bowl full of coccoons at the same time.The silk is coiled into hanks or skeins, and in this form is imported into this country; from these hanks it is wound off on to large six-sided wheels called “swifts,” and from these on to bobbins or reels; it is then wound off from two or three of these bobbins on to one other bobbin, the threads of silk being laid side by side, and in this process a twist is given to it in one direction and two of these wound on to another receiving a twist in an opposite direction, this forms a fine cord called “organzine,” which is used by the silk weaver in the same way that yarn is by the cotton weaver. The short and broken pieces are carded and spun like cotton, and is called floss silk. The raw silk is of a bright buff or golden yellow color, but there are some kinds which are white.
INDIA-RUBBER.
India-rubber or Caoutchouc which was, a short time back, used only for the very insignificant purpose of rubbing out pencil marks, is now used for almost innumerable purposes. India-rubber is the solidified juice of several trees, such as the Siphonia, Jatropha Elastica, Ficus Elastica, &c., the juice is got by making incisions in the trunk of the trees during winter and collecting the juice, which is caoutchouc combined with water, in the form of a milky thick fluid, the water is then allowed to evaporate and the India-rubber remains. It is brought here in all sorts of shapes, and is purified before it is fit for commercial use by washing in warm water or steaming; it is then cut into pieces and put into a kneading machine which cuts and works it together with such rapidity that it becomes quite hot and the pieces join into one mass. After having undergone every kind of torture that can be well imagined in the form of cutting, tearing, and squeezing, it is finally compressed in a square cast iron mould, where it is kept for a time, and then is fit for any use it has to be applied to. What is called vulcanized India-rubber is produced by incorporating it with powdered sulphur, or some substance containing it, as sulphuret of antimony, or the vapour of sulphur is kneaded into the mass; this vulcanized rubber is very elastic and does not harden by cold. Waterproof fabrics are made by stretching the stuff to be waterproofed on a frame, at one end of which is a partition having a slit in it, through which it is drawn, after having been smeared with a solution of India-rubber in naptha; the slit is so narrow that it scrapes off all superfluous caoutchouc, it is then dried in the air.
GUTTA-PERCHA.
Gutta-percha is a substance possessing many useful and valuable properties; it was unknown in Europe until within a very recent date, though it is said to have been in common use, for a long period previous to our discovery of its utility, amongst the natives of the Indian Archipelago, chiefly for making axe-handles. It is the concrete juice of a large tree, supposed to be the Isonandra Gutta, and is brought to Europe in irregular masses of a brown color, and contains various impurities which are easily got rid of by working it in hot water. Gutta-percha possesses the desirable properties of being solid, slightly elastic, not brittle, and very tough, capable of being melted at the heat of boiling water, and being drawn out or moulded into almost any form; it resists the action of water and spirits, unless very strong, oils, alkalies, and weak acids, but spirits of turpentine, chloroform, and naptha, each dissolve it. A substance which has so many valuable properties as these, of course enters into a multiplicity of forms and uses.