204 INDIA-RUBBER OK CAOUTCHOUC.— Elastic Thread.

method of preparing sheet india-rubber by cuttingslices from a previously prepared block, the mass ofmaterial was firmly secured in a machine, having astraight steel blade with its edges slanting down-wards on to the surface of the block, which wasraised regularly as the cutting progressed. By thehorizontal vibrations of the blade the cake of india-rubber was rapidly cut into sheets of anydesired thick-ness, from those sufficiently thin to cut into threads,to those destined to be subsequently recut intosquare or oblong blocks for the use of the draughts-man. During the cutting the knife as well as thesurface being cut have to be kept continually wetby a stream of water.

We are informed by Foster and Williams ofBermondsey , the well-known rubber manufacturers,that the strongest sheet india-rubber is still obtainedby cutting from solid blocks of the compressedmaterial, the largest sheets thus made being about

8 feet long by 1 foot 6 inches in breadth. Muchlarger sheets, however, can be obtained by thepassage of a block of purified material fresh fromthe masticator between highly polished steel rollersheated to about 200 Fahr. The sheets so obtained,however, are not so strong as those obtained fromsolid blocks by cutting. The rolling machines arecalled “calenders,” and the distance between therollers is regulated by an attached screw mechanism,so that by this means any thickness of sheet rubbercan be produced. Sometimes the rolling is conductedon cloth, but this is not an invariable practice. Theoriginal rollers used weighed only about 2 or 3cwts. each, whereas the weight of each now amountsto 3 or 4 tons, the whole machine being often asmuch as 50 tons in weight. The whole apparatusis represented at Fig. 5. The great advantage ofthe modern method of making sheet india-rubberlies not only in the comparative facility of production,

Fig. 5.

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but likewise in the fact that the size of the sheets isnot limited, as in the method of cutting from solidblocks. Fragments of purified india-rubber placedin the rolling mill (as it may be termed) unite withthe greatest facility and produce perfect sheets, sothat the material can be fed in continuously betweenthe rollers, and the sheet produced wound off at theother end. From this sheet india-rubber all sortsof objects are fashioned, principally by hand, withthe aid of the proper moulds and machinery.

Manufacture of Elastic Thread .—This is now amost important branch of industrial manufacture,carried on in London principally by Messrs. Warneof Tottenham, with -whom it is quite a speciality, andalso by the firm of Mackintosh & Co. India-rubberthread is very extensively used for making elasticfabrics, braces, garters, &e. One of the best descrip-tions of thread is a red vulcanized material preparedby Messrs. Waiine by the aid of special machinery.

There are three methods of producing thread fromindia-rubber; the first two are strictly mechanical,while the third, although also in a sense mechanical,is of a totally different description, and is, we believe,not used at the present time. These methods areas follows:—

1. Cutting the material from sheets or bands bythe action of a knife.

2. Obtaining the thread from sheets or bands bytwo or more knives working together, after themanner of scissors.

3. Manufacture of round thread by making theindia-rubber into a paste by the addition of a limitedquantity of a suitable solvent, and subsequentlysqueezing the paste thus produced through smallorifices of the required diameter.

Of these three modes the second is that which ismost used, but we shall now give a short descriptionof each in rotation.