Pitch is the name for any number of resins with high viscosity (about 100 billion times more viscous than water) that appear solid and will shatter if hit, but also flow at room temperature, albeit very slowly. Pitch can be derived by the distillation of wood, coal, plant resins or petroleum in which case it is called bitumen. Pitch is a point in a continuum of substances such as asphalt, tar and something called slime. Tar for example, is more fluid than pitch and slime is liquid at room temperature. Glass also inhabits the same strange world of solids that flow, though it takes centuries for it to do so appreciably.*
Pitch has been know since time immemorial and is mentioned in a particularly Life of Brianish line in the story of Noah and the ark:
“Make thee an ark of gopher wood; rooms shalt thou make in the ark, and shalt pitch it within and without with pitch.” BibleGenesis 6:14
The ancients had access to pitch from boiling the
bark of
trees such as
birch and from
natural bitumen which can be found sometimes freely seeping out of the ground, and also in bitumen impregnated
sands called
tar sands or
oil sands. The use of pitch to waterproof ancient craft is one of the technological innovations that helped establish
maritime commerce and the first steps to a
global economy.
One of the most curious uses of pitch is the pitch drop experiment started by the first physics professor at the University of Queensland, Australia, Thomas Parnell. The experiment was started in 1927 and is still going on today: the good professor heated a sample of pitch and poured it into a funnel with a sealed stem. After allowing the sample to settle for three years, the stem of the funnel was cut and the pitch was allowed to flow onto a waiting beaker below. The whole contraption is kept in a cabinet in the foyer of the physics department and to this date, eight drops have fallen into the beaker. No one has been around to witness any of the drops though now a webcam keeps constant vigil. The eighth drop fell recently, but unfortunately the camera had malfunctioned.
*call points out correctly as it turns out that I have been duped along with a lot of other folks by this old wife's tale. Glass is not a liquid after all. There are a number of references on the web to an article that dispels the myth: Antique windowpanes and the flow of supercooled liquids, Robert C. Plumb,(Worcester Polytech. Inst.), Journal of Chemical Education, 66(12), 994-6, 1989.
The Pitch Drop Experiment,http://www.physics.uq.edu.au/pitchdrop/pitchdrop.shtml,8/14/2004
Pitch (resin) Wikipedia,http://en.wikipedia.org/wiki/Pitch_%28resin%29,8/14/2004