The manipulation of pure sheet rubber is simple, yet is liable to lead to disappointment. When two pieces are laid face to face and cut across with a sharp knife, or scissors, the edges will adhere with considerable tenacity. This may be increased by applying some thick solution of india rubber in a volatile solvent, and by manipulating the sheets so as to bring the entire surfaces of the cuts together. Finally the material may be charged with sulphur by absorption or by Parkes’ process, and cured in a glycerine or calcium chloride bath, all of which are described in chapter XI. The same treatment will affect the cement used in making the joint also, bringing about its vulcanization.

Such in a few words is the main process in the treatment of this class of goods. Where it is desired to prevent adherence, soapy water or powdered talc is used.

Adherence may be produced between the surfaces of the sheets if they are clean, by pressure and a little warmth. The method of making toy balloons will give an example of how the article is dealt with by the manufacturer.

A pile of pieces of masticated sheet rubber is made. Every piece has one side coated with powdered talc, and two talc-coated sides are placed in contact in each pair. As they are piled up, the outer surfaces of each pair are moistened with water. A steel punch or die, pear shaped in outline, is used to cut down through the pile, cutting all the pieces into that shape.

The pile is then taken apart in pairs. The separation takes place between the wet surfaces, the edges of each pair adhering slightly so as to enclose the talc-coated surfaces. The neck is opened if necessary. A rather weak or thin solution of india rubber in benzole is now brushed over the freshly cut edges. By pulling out the centre of each piece the edges are brought into contact, and adherence is produced.

If the Parkes process of vulcanizing, chapter XI., is employed they are cured to the slight extent necessary upon a tray coated with talc. The balloons are then ready for inflation.

They are rather delicate articles to make except for immediate use as the thin material is liable to become over vulcanized.

In the chemical laboratory sheet rubber can be used for covering the ends of glass stirring rods. These answer very nicely for cleaning out from beakers the last particles of a precipitate. The sheet is cut of proper size and is bent around the end of the rod and cut off close with a pair of scissors. It adheres where cut. It is then pinched with the fingers to bring the edges into better contact and the operation is complete. A slight heat makes it adhere better.

To connect glass tubes in setting up laboratory apparatus the same material was formerly used. It was wrapped around the joint, tied with thread and slightly warmed. At present this form of connection is wholly displaced by ready made rubber tubing.

It is interesting to observe in all articles made from this sheet the marks of the original cutting knife. These may be observed in inflated balloons, as parallel lines running all over the surface, and magnified by the expansion due to the inflation.