Washing and Drying.—The first part of the washing process consists in throwing the raw article into large iron tanks, containing water, sometimes heated by injected steam for a few hours, so as to soften the rubber, and facilitate its nutting up before passing through the washing-machines or rollers. This preliminary boiling serves another purpose : as indiarubber floats easily in water, any portions containing clay, sand, iron, or other heavy matters, sink to the bottom, and are at once detected. It is a common thing to find, instead of these heavier matters. rags, nuts, leaves, and wood concealed in the mass; these portions are not washed with the other, hut are kept by themselves, as they require more careful cleansing. The adhering dirt should be scrubbed off, if necessary. The softer kinds of rubber must be treated with cold water, and not boiled.
When removed from the tank, the masses of rubber are cut open with a large knife, if they can bo sufficiently examined with one incision, which is the case tho'se rubbers which are met with in smaller masses ; if in large bulky masses, as the Pani, and negrohead, and those which become massed by agglutination, it is either cut up by a revolving circular knife, or by an ordinary long-bladed knife. A eircular knife is the most expeditious, but is, of course, more dangerous in case of stones being concealed in the rubber. Whichever method is adopted, this cutting up is either performed by the foreman of the washing-shop, or under his immediate inspection, for it not unfrequently happens that a classification is necessary, even with a package of the very best description. It is then passed to the washing-rollers, or washing-machines.
The washing-machine consists essentially of two grooved or corrugated iron rollers, working in journals, and adjustable by means of a screw, working through the front part of the iron framework. Each roller has a strong pinion keyed to one end, and the pair are worked by a strong toothed wheel, attached to a shaft, which drives several machines. The rollers revolve in opposite directions, thus drag the rubber through, while a jet of cold water—hot is sometimes necessary—falis upon it, preventing heating from friction, and diasolving out the soluble matters, as gum, sugar, and salts, existing in the natural juices of the plant. Under the machine, is a wooden box, or frame, with a perforated zinc bottom, to let off the water, and prevent the escape of small fragments of rubber.
The speed at whioh these machines are driven is not a matter of much importance. Sometimes two speeds are employed, generally obtained by working two sets of machines from separate shafting and gearing, and better by having rollers of larger diameter. By giving extra strength
to the machine, so as to use larger and longer rollers, labour is economized. The rollers should not exceed 12-18 in. in length ; for very fine washing, 9-10 in. will suffice, as they are liable to open out by springing.
The rubber is first passed through a few times with the rollers tolerably wide apart, and as the pieces of wood, hark, &c., are washed out, the rollers are gradually closed, or the rubber is finished off in another machine, with finer rollers set closely. With careful washing, it is almost possible to bring the lower descriptions of S. American, Bornean, and a few others, to a degree of cleanliness equal to that of Pant rubber. Formerly, washing-rollers were enclosed in an iron box or case ; now, a wooden hood surrounds the machine, when treating such rubbers as are liable to fly about.
A form of washing-machine which has become almost obsolete may be referred to, as it is especially useful for washing up short or crumbled rubber. It consists of a fluted spindle or axis, with rough teeth, revolving in a strong iron box ; the rubber is supplied through an aperture in the top, and is removed by opening the front, which works on a strong bolt as a hinge. This rubber is dried on canvss trays, or strewn on a clean floor.
The ordinary washed rubber comes away from the machines in long sheets, with rough surfaces, and is dried by being hung up for some days in drying-rooms, heated to about 32° (90° F.) by steam-pipes. The influence of direct sunlight on the rubber is prevented by painting the windows white or yellow. Some rubbers cannot be obtained in sheets like this, and are too soft for banging up ; these are dried on the floors. The rubber Must not come into contact with the steam-pipes; when thoroughly dried, it is taken down, and stacked away on shelves, in a dry snd moderately warm store-room, for seasoning, or for immediate use. Washed rubber improves by stacking, and for insulating purposes, ebonite, and the finer classes of goods, it is preferable, There are great differences in the degree of loss of moisture and impurities even from the same description of rubber ; thus, old Para rubber will suffer a loss of 7-12 per cent., whilst new or green rubber will frequently lose 15 per cent,, or even more. Negrohead of good quality may be taken as losing 20-25 per cent. ; 15 per cent. was formerly a fair figure, but the practice now is to pack this rubber in very large masses, and frequently to empty into it non-inspissated juice, so that it reaches the English markets quite saturated.