474 



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 in- 

 genious methods to overcome special difficulties are practised. 

 The process of making india-rubber 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 oval 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 carbonate 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 completely 

 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 convas, 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 for wearing apparel. This is one 



