Plastic Bituminous

The resin is fairly soluble in alcohol, ether and chloroform and is decomposed by nitric acid. It becomes thermoplastic at temperatures above 150°C and decomposes at a temperature rather below 300°C, yielding an oil of amber and leaving a residue known as amber colophony or amber pitch. 

X-ray evidence shows the material to be completely amorphous as might be expected from such a complex mixture. The specific gravity ranges from 1.05 to 1.10. It is slightly harder than gypsum and therefore just not possible to scratch with a fingernail. Yellow in colour, it is less brittle than other hard natural resins and may therefore be carved or machined with little difficulty. The refractive index is 1.54. 

Amber has been a much prized gem material for many millennia and has been found at Stonehenge, in Mycenaen tombs and in ancient European lake dwellings. In modem times it is used for beads and other ornaments, cigarette holders and pipe mouthpieces. 

At one time the small fragments of amber produced during the fabrication and machining operations were used to produce varnishes. In 1880 they were first used in the production of Ambroid. This is made by pressing the fragments in a hydraulic press at temperatures somewhat above 160°C. The moulded product has a close resemblance to amber. A form of extmsion has also been used to produce amber rods for subsequent conversion into pipe and cigarette-holder mouthpieces. 

Although generally ignored in plastics literature the bituminous plastics are still of interest for specific applications. The moulding compositions consist of fibrous and mineral fillers held together by a bituminous binder together with a number of minor ingredients. 

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The largest outlet for the bituminous plastics has been for automobile battery boxes. Bituminous battery boxes do, however, have a susceptibility to electrical breakdown between the cells and in Europe their use has been mainly confined to the cheaper batteries installed initially in new cars. Bituminous compositions have also been used for toilet cisterns and to some extent for cheap containers. They are no longer important. 

Copper and its alloys can be safely buried in most soils, although high corrosion rates have been observed when cinders and acidic peat are present in the soils. When high corrosion rates are expected it is preferable to protect the samples with bituminous, plastic or paint coatings. When brasses are used dezincification problems may be encountered and hence their use should be avoided, unless high sulfide concentration is present in the soils. 

Cold molding . A process similar to compression molding except that no heat is applied during the molding cycle. The formed part is subsequently cured by heating and cooling. A-stage phenolic resins and bituminous plastics are sometimes molded by his process. 

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