Rubber perishing

Lead-covered wiring was superseded by the tough-rubber-sheathed (TRS) system where the VRI conductors were contained in a tough rubber sheath with an uninsulated protective conductor. This solved the earth continuity problem but the wiring became a fire hazard when the rubber perished. After World War II, PVC was introduced and replaced the rubber for both insulation and sheath and, apart from some teething troubles in its early years, it is now satisfactory and appears to have a very long life. As it burns less readily than rubber it is a lesser fire hazard. 

Lignosulfonates have recently been tried as a filler for rubber but are slightly less efficient than carbon black, the cheap conventional filler with which it must compete. However, it is conceivable that lignin could increase the stability of rubber to ozone, the natural reagent which causes vulcanized rubber to "perish. ... 

Rubber becomes brittle in cold weather and tacky in hot weather, and it is odorous and perishable. It also has very low tensile strength and low resistance to abrasion. One of the major advances in the improvement of rubber was in the discovery by Charles Macintosh in Scotland in 1820 that coal-tar naphtha is a cheap and effective solvent for rubber. He placed a solution of rubber and naphtha between two fabrics, and in so doing he covered up the sticky or brittle surfaces that had been common in earlier single-texture garments treated with rubber. Macintosh patented the process in 1823. These double-textured waterproof cloaks, which were first introduced to the public in 1824, have been known ever since as mackintoshes. 

Rotational entropy, 36 Rotation frequency, 8 Rubber natural, 323 perishing of, 328 synthetic, 189, 322 vulcanisation, 323... 

Consequently, substantial concentrations of ozone can accumulate around electrical equipment and photocopying machines. Rooms containing these must be well ventilated, since ozone is toxic and can cause headaches and irritation of the mucous membranes, even in low concentrations. It has been suggested that ozone may be the cause of the excess death rate from leukemia (blood cancer) in electrical workers. Ozone is also extremely damaging to plant life, much more so than acid rain (Sections 8.4 and 8.5). It also attacks rubber and may cause rubber insulation on electrical equipment to perish rapidly. 

The thermometer is first dipped in the sulphuric acid, and then the drop of acid which clings to the bulb is smeared on the side of the capillary tube containing the substance. The capillary tube is then made to adhere to the thermometer (Fig. 6) by capillary attraction, so that the substance in the tube is just opposite the bulb of the thermometer. This method is much better than using a rubber band, which is apt to perish in the sulphuric acid fumes, and gives rise generally to a speedy discoloration of the acid. 

Most materials have a finite life. Metals corrode they can also suffer from fatigue. Wood rots, and concrete cracks or suffers from various chemical degradation processes. Natural rubber can perish as a result of ozone attack. All these materials have been around for long enough for us to know and make allowance for their weaknesses. 

Solid carbon dioxide is used quite extensively to refrigerate dairy products, meat products, frozen foods, and other perishable foods while in transit. It is also used as a cooling agent in many industrial processes, such as grinding heat-sensitive materials, rubber tumbling, cold-treating metals, shrink fitting of machinery parts, vacuum cold traps, and so on. 

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