The bottles, and masses, and fragments, as imported, have much inequality in texture, and are, moreover, contaminated with much dirt and refuse. To separate these, the India-rubber is first cut into very small fragments, and then steeped in warm water, by which the dirt is precipitated. The fragments are dried, and are then thrown into a kind of kneading machine, where immense pressure is employed to bring them to one homogeneous mass. The India-rubber, though put in cold, becomes so hot by the agitation that it could not be safely touched by the hand; it is necessary to supply the machine with cold water, which is made nearly to boil by the caloric driven out of the elastic mass. So thoroughly is the mass pressed, rolled, pricked, cut, and kneaded, by the severe turmoil which it undergoes, that all dirt, air, water and steam are expelled, and it presents the appearance of a dark colored, uniform, smooth mass. It is put into cast iron moulds of great strength, and brought, by hydraulic or screw pressure, to the form of blocks, slabs, or cylinders, according to the purpose to which it is to be applied.
MACKINTOSH CLOTH.
The manufacture of the Mackintosh cloth is a singular one. The material is merely two layers of cotton cemented with liquid India-rubber; but the junction is so well effected, that the three become to all intents and purposes one. The stout and well-woven cloth is coiled upon a horizontal beam, like the yarn beam of a loom; and from this it is stretched out in a tight state and a nearly horizontal position. A layer of liquid or rather paste-like solution is applied with a spatula, to a considerable thickness, and the cloth is drawn under a knife edge, which scrapes the solution and diffuses it equally over every part of the cloth, which may be thirty or forty yards long. The cloth is then extended out on a horizontal framework to dry; and, when dried, a second coating is applied in a similar way; and a third and fourth may be similarly applied if necessary. Two pieces, thus coated, are next placed face to face with great care, to prevent creasing or distortion; and, being passed between two smooth wooden rollers, they are so thoroughly pressed as to be made to unite durably and permanently. Cloth, thus cemented and doubled and dried, may be cut and made into garments which will bear many a rough trial, and many a deluging before rain or water can penetrate.
INDIA-RUBBER CUTTING PROCESSES.
It is as a sheet and as a thread that India-rubber meets its most extensive application; and both of these are made by cutting from the blocks and slabs. A block is cut into sheets by an ingenious machine, in which a sharp knife-edge has a rapid vibratory motion in a horizontal plane, so adjusted as to cut a thin film from a block of India-rubber supplied to it by a steady motion. The knife requires to be kept cool by a flow of water, or it would adhere to the India-rubber. In this way thin sheets may be cut, or thicker sheets from which stationers’ India-rubber may be obtained, or sheets of any thickness, great or small, according to the purposes required.
The separation of the material into shreds or narrow strips is a very pretty operation, exhibiting much nicety of manipulation. A continuous strip may be cut from a bottle or any other curved mass of the India-rubber. The bottom of the bottle is cut off, and is pressed into a round and tolerably flat form. The cake thus fashioned is fixed to the end of the horizontal shaft, or lathe-axis, and is made to revolve with great rapidity; and while so rotating, a circular knife, rotating at high speed, cuts through the substance, and advances steadily towards the centre of the disc; thereby separating the disc or cake into one continuous spiral thread. This thread can be easily drawn out straightly, and can even be separated into two or more finer threads, by drawing it through a hole where one or more sharp-cutting edges encounter it. If a bottle or any other hollow piece of India-rubber can be drawn over a cylinder of uniform diameter, it may be cut into a continuous thread, by a modification of the same machine; the cylinder being made to revolve, a steel cutter is placed against it, and as the cylinder has a slow longitudinal motion given it, the gum is cut spirally from end to end—just on the same principle as a worm or thread is cut on a bit of iron by the screw-cutting machine. Machines of this kind were invented in France more than twenty years ago; but the machines used in our own country are of English invention and of later date.
INDIA-RUBBER LIQUID.
When once it was discovered that India-rubber may be dissolved in petroleum, in naptha, or in oil of turpentine, it was speedily seen that a new and extensive sphere of utility was given to it. The coarsest pieces, as imported, the waste from the kneading operations, and the parings and cuttings from other manufacturing operations, are placed in a close iron vessel, to which the liquid solvent is added. A brisk agitation is kept up, and the heat thereby generated in the elastic gum warms the liquid and increases its solvent power, until at length the whole of the gum is dissolved. This operation is conducted on a somewhat extensive scale; for the iron vessel is large enough to contain more than half a ton of India-rubber, which requires three days of constant agitation for complete solution. The liquid thus produced has a consistency which fits it to be used as a varnish, or as a water-proofing medium, or as a cement, or for many other purposes which the sagacity and self-interest of manufacturers have enabled them to discover.
INDIA-RUBBER BRAIDS AND WEBS.
If we glance among the stores of the India-rubber manufacturers and retailers at the present day, we find the braids and cords, webs and bands, form no inconsiderable portion of the wares exposed for sale. These, in most cases, require that the India-rubber should be first made into blocks or cakes, next cut into sheets, and then separated into threads, or cords, or narrow strips. Supposing these preliminary cuttings to be effected, the making of braids and webs is exceedingly curious, for it involves a combination of the India-rubber with other materials. Let us briefly trace the processes. In the first place, the narrow cords are stretched by a kind of wheel, and kept extended till nearly deprived of their elasticity, and till they form a thread of the desired thickness. The thread is then put into a braiding machine which is a complicated and very ingenious apparatus, whereby a sheathing of cotton, silk, flax, or worsted, is wound round the India-rubber thread. In such a machine several threads are twisted round each other, from three to nearly thirty in number; each thread has its own bobbin, and all the bobbins revolve round a common centre, giving out their threads in the proportions and order required. Generally speaking, the braiding machine is employed in making stay-laces, braid, upholsterers’ cord, &c.; but it is also applicable to making the numerous elastic cords and webs which owe their elasticity to India-rubber. When an envelope of cotton, silk, flax, or worsted, has been given to the thread of India-rubber by the braiding machine, the threads are laid as warp in a loom, and woven into the required kind of web, whatever it may be. Then comes a curious development of the properties of the material; in the preliminary stretching, the India-rubber was made somewhat stiff and unyielding; but by now exposing it to the action of a hot smoothing iron upon a table, the elasticity is restored, the riband or web contracts in length, and the sheathing or envelope corrugates or wrinkles up on the surface. The web thus produced is very soft and elastic. The warp threads may be alternated with others of non-elastic character; and the weft-threads may be either elastic or non-elastic, so that any desired degree of elasticity may be obtained.