Oct. 1906.] 



295 



Saps and Exudations. 



tedious ; the principal underlying all processes is the same— namely, moulding 

 plastic dough and then reproducing the elasticity and tenacity of the rubber goods 

 by heat and vulcanisation. 



29. Rubber goods that are "built up" fall naturally into two classes 

 according to their being pure dough or compounded with other materials, as in 

 the case of outer covers for tyres, hose piping, rubber belting, etc. The general 

 mode of treatment is the same in all cases, and it is a mixture of joinery and 

 tailoring. The dough is soft and plastic and so can be rolled to any thickness, 

 cut to any shape, and applied to the goods in any manner. The dough contains 

 raw rubber and therefore is adhesive ; cut edges of it can be pressed into 

 contact, and that with the greatest ease, if the edges or surfaces are previously 

 moistened with any rubber solvent. The tools necessary for tise in this 

 work are consequently of the simplest— a keen knife or stamps for cutting 

 shapes, a squeejee for pressing surfaces into contact, and a pot of benzine with a 

 piece of cloth as a sponge for moistening, with this solvent, edges to be stuck 

 together. The goods built up in this way are, as would be expected, of extremely 

 diverse character, and in some instances most ingenious methods to overcome 

 special difficulties are practised. The process of making Indiarubber balls is a case 

 in point. Rubber dough in the form of sheets is cut into oval pieces of precise size 

 with a knife and a metal shape, the edges being cut bevelled. Three of these ova 

 pieces are applied together by their edges which are firmly cemented with the 

 assistance of a little benzole, forming very roughly a hollow ball. An aperture of 

 about an inch in length is left between the edges of two of the pieces, a small lump 

 of pure masticated rubber is stuck to the inside of one of the pieces, and the position 

 of this indicated on the outside with a spot of paint. A pinch of ammonium carbon- 

 ate is then put inside the ball, and after examining the joints inside the ball with 

 the aid of a little electric glow lamp the aperture is sealed up. The balls are then put 

 into moulds and vulcanised by heat. The object of the ammonium carbonate is here 

 seen. This substance on heating to the temperature used in vulcanisation is com- 

 pletely vapourised, and this vapour exerts some pressure inside the balls, blowing 

 them out tightly against the spherical moulds in which they are being heated, 

 rendering the shape exact to the mould and assisting in ensuring perfection of the 

 joints ; on cooling the solid ammonium carbonate is again reformed and the balls are 

 limp and under no pressure when removed from the moulds . A hypodermic needle 

 connected with air under pressure is then thrust into the ball at the point where 

 the lump of raw rubber was stuck inside. The compressed air is turned on and the 

 ball inflated to its proper size, as shown by a gauge. On withdrawing the needle 

 the aperture left in the lump of rubber inside, which contained no sulphur and 

 which is therefore unvulcanised and sticky, at once closes and seals up the hole, a 

 dab of solution is pricked into the hole in the outer cover to close this up also, and 

 the ball is ready for use, ready to be painted and enamelled in gaudy colours and 

 sold as a toy, Or to be covered with cloth and become a tennis ball for men. Most 

 hollow air-tight rubber goods in one piece are prepared in this way, the presence of 

 a lump inside may be taken as a certain indication of it. Hose pipes are constructed 

 by being built up round iron tubes, 60-100 feet in length. Strips of canvas, coated 

 with a film of rubber, layers of dough on canvas, and again canvas coated 

 with a film of rubber are wrapped simply, without any spiral twisting, in layers 

 over the inner core : the layers are all stuck together and squeejeed into a firm 

 union, and then vulcanised. To extract the inner iron tube from the vulcanised pipe 

 air is forced in between this tube and the outer hose pipe, which can then be easily 

 slipped off the iron tube, 



SPREAD AND SHEETED GOODS. 



30. This class includes all the waterproof fabrics from the coarse and heavy 

 waterproof sheet of which the basis is a canvas, to the lightest and thinnest cloth 



