Pitch (resin)

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The pitch shown in this pitch drop experiment has a viscosity approximately 230 billion times that of water.

Pitch is an archaic name for any of a number of viscoelastic, semi-solid polymers. Pitch can be made from petroleum products or plants. A natural semi-solid form of asphalt (also called bitumen) was, in the past, sometimes referred to as pitch. Pitch produced from plants is also known as resin. Some products made from plant resin are also known as rosin. Other archaic names for natural asphalt include "tar" and "asphaltum".

Pitch was traditionally used to help caulk the seams of wooden sailing vessels (see shipbuilding). Pitch was also used to waterproof wooden containers, and is sometimes still used in the making of torches. Petroleum-derived pitch is black in colour, hence the adjectival phrase, "pitch-black".

Viscoelastic properties

Tar pitch is a viscoelastic polymer. This means that even though it seems to be solid at room temperature and can be shattered with a hard impact, it is actually fluid and will flow over time, but extremely slowly. The pitch drop experiment taking place at University of Queensland is a long-term experiment which demonstrates the flow of a piece of pitch over many years. For the experiment, pitch was put in a glass funnel and allowed to slowly drip out. Since the pitch was allowed to start dripping in 1930, only eight drops have fallen. It was calculated in the 1980s that the pitch in the experiment has a viscosity approximately 230 billion (2.3×1011) times that of water.1 The eighth drop fell on 28 November 2000, and the ninth is expected to fall at some point in 2014. Another experiment was begun by a colleague of Nobel Prize winner Ernest Walton in the physics department of Trinity College in Ireland in 1944. Over the years, the pitch had produced several drops, but none had been recorded. On Thursday, July 11, 2013 scientists at Trinity College caught pitch dripping from a funnel on camera for the first time.2

Production

The heating (dry distilling) of wood causes tar and pitch to drip away from the wood and leave behind charcoal. Birchbark is used to make Birch-tar, a particularly fine tar. The terms tar and pitch are often used interchangeably. However, pitch is considered more solid while tar is more liquid. Traditionally, pitch that was used for waterproofing buckets, barrels and small boats was drawn from pine. It is used to make Cutler's resin.

See also

References

  1. ^ The Pitch Drop Experiment
  2. ^ "Trinity College experiment succeeds after 69 years". RTE News. Retrieved 18 July 2013. 

External links








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