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 r 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 
