The first characteristic which one associates with rubber is its unique property of withstanding extraordinary deformation without permanent alteration. No other substance exists which can be stretched to ten times its original length and will yet return to its original shape unchanged. This characteristic, in conjunction with its other properties, accounts for the use of rubber for a vast number of purposes in which a more rigid material would utterly fail. The importance of a substance which is at once strong, pliable and extensible, needs no emphasis. Apart from obvious applications, such as aeroplane shock absorber cord, one has only to consider the difficulty which would exist in finding some material other than rubber for the air container in a pneumatic tyre to appreciate that these properties alone would suffice to render it an almost indispensable product. Other plastics, such as linoleum, celluloid, glue, casein, etc., have their special uses, but their scope is greatly limited by comparative lack of extensibility.

Not only does rubber withstand exceptional deformation without change, but it is at the same time tough and-particularly when suitably compounded-calls for the expenditure of a considerable amount of energy to stretch or compress it. This remarkable extensibility, combined with a tensile strength approaching that of metals, confers on rubber the power of storing energy to a degree far exceeding that of any other known solid material, and explains the wide use to which rubber has been put, in connection with mechanical transport, as a means of reducing vibration and shock. The use of solid tyres on lorries, and of springs and buffers on railways, may be cited as familiar examples. It seems probable,, however, that the employment of rubber for the purpose of reducing vibration is likely to obtain still wider recognition, especially in connection with the isolation of running machinery, and, even to a greater degree, as a means of minimising the effects due to heavy and rapidly moving traffic on the roads.

Closely connected with the remarkable energy-storing capacity of rubber is its unique power of resistance to abrasion, due partly to its inherent cohesion and partly to its ease of deformation.

In spite of obvious examples in every day use. the extraordinary wearing qualities of rubber are not as widely appreciated as they deserve to be, and probably few persons have given a thought as to how other materials would behave if subjected to the same conditions as a motor tyre tread. The fact that rubber outlasts leather on shoes must be familiar to all, and as an example of its durability as a floor covering, an instance may be cited of a factory staircase in which rubber-covered steps are still perfectly sound, while those made of stone have been twice renewed. This property of rubber is attracting increasing attention for a variety of technical applications, and it will suffice to refer to three such instances, namely, gloves and tubing for sand-blast work, linings for ball mills, and conveyer belting for ore and coal-all uses in which resistance to severe abrasion is of the utmost importance. Other excellent wa terproofing agents are known but not one possesses the combination of properties which makes rubber an almost ideal substance for coating and joining various textile materials. An oilskin garment, for example, is perfectly satisfactory so far as resistance to water is concerned, but the comparative lack of elasticity of the oil film renders the material liable to tear, while the lack of strength of oil proofing makes it quite unfit for use in building up composite articles such as hose and belting, for which rubber is so successfully employed.

The uses of rubber for the purposes of retaining or excluding liquids or gases are many and varied, and the following examples may be quoted at random : miners' boots, diving dresses, balloon fabric, and oil and air brake hose. So far reference has been made only to the physical properties of rubber, and in conclusion we may refer to some applications due more particularly to its chemical characteristics.

Of the problems in a chemical works, that, of handling dilute acid liquors is amongst the most difficult. The corrosive action of such solutions-particularly those containing hydrochloric acid- on unprotected metal necessitates the use of enamel or the substitution of gass, earthenware, or resinous wood for metal containers. The effect of steam and acid fumes on leather belting is, moreover, disastrous. In such circumstances the resistance of rubber to alkalis and dilute acids becomes a property of great technical value. It supplies hose and transmission belting which will withstand these severe conditions of usage, ebonite fittings to replace metal, and boots, gloves, and overalls to protect the workers from contact with corrosive liquids. Gutta percha vessels have long been employed for the storage of hydrofluoric acid, the use of ebonite for battery boxes is a common practice, and the general adoption of rubber-lined tanks and transport waggons for certain purposes is probably only a matter of time.

Owing to its unique physical properties and the wide diversity of its applications, rubber in some form or another is to be found in the service of man in every quarter of the globe. It is, therefore, called upon to retain its remarkable properties under every conceivable condition of climate from the Arctic Circle to the Equator. Its almost universal use is testimony to the fact that rubber is far from being an unstable substance, and numerous instances are on record of samples having been found in sound condition after the lapse of a generation.

Much depends, however, on the conditions under which rubber goods are stored and used, and due regard must be paid to these points if satisfactory life and service are to be expected, especially in tropical climates.