http://www.ucl.ac.uk/sts/staff/chang/boiling/index.htm The Myth of the Boiling Point
Hasok Chang Department of Science and Technology Studies University College London 18 October 2007 Introduction We all learn at school that pure water always boils at 100°C (212°F), under normal atmospheric pressure. Like surprisingly many things that "everybody knows", this is a myth. We ought to stop perpetuating this myth in schools and universities and in everyday life: not only is it incorrect, but it also conveys misleading ideas about the nature of scientific knowledge. And unlike some other myths, it does not serve sufficiently useful functions. There are actually all sorts of variations in the boiling temperature of water. For example, there are differences of several degrees depending on the material of the container in which the boiling takes place. And removing dissolved air from water can easily raise its boiling temperature by about 10 degrees centigrade. The fickleness of the boiling point is something that was once widely known among scientists. It is quite easy to verify, as I have learned in the simple experiments that I show in this paper. And it is still known by some of today's experts. So actually the strange thing is: why don't we all hear about it? Not only that, but why do most of us believe the opposite of what is the case, and maintain it with such confidence? How has a clear falsehood become scientific common sense? I first became aware of this whole issue a few years ago, in the course of working on my recent book Inventing Temperature (New York: Oxford University Press, 2004), a historical and philosophical treatise on thermometers and the temperature concept (read theIntroduction and table of contents of the book). The old thermometer whose photo I have put on the cover of the book speaks volumes (click on the picture for a larger version). This instrument, dating from the 1750s, is preserved at the Science Museum in London; the glass stems have broken off, so all we have is the frame, which shows four different scales on it. The third one is the familiar Fahrenheit scale. (The second one, due to Delisle, is "upside down", with 0° at the boiling point and increasing numbers as it gets colder; read more about such scales on pp.160-162 in Inventing Temperature.) There are two boiling points marked on this thermometer. At the familiar 212°F it says "water boyles vehemently". Down at about 204°F it says "begins to boyle". What is going on here? You may think that the artisan who made this thermometer must have been pretty incompetent on scientific matters. But it turns out that this thermometer was the work of George Adams, official scientific instrument-maker to King George III. And the idea of two boiling points actually came straight from Isaac Newton, whose temperature scale published in 1701 was indeed the first of Adams's four scales. <continues> http://www.ucl.ac.uk/sts/staff/chang/boiling/index.htm
