This phase diagram supports my observation that iodine melts and vaporizes, rather than sublimating.
(You can find this image at the bottom of a chemistry test by Professor Chris King of Troy State University.)
The diagram is also supported in a paper by V. V. Brazhkin (with S.V. Popova, R.N. Voloshin, Pressure-temperature phase diagram of molten elements: selenium, sulfur and iodine, Physica B 265, 64-71, 1999.), this University of Massachusetts chemistry worksheet, the CRC Handbook of Chemistry and Physics, the Merck Index as well as my own observations.
None-the-less, most high school and college chemistry classes teach that iodine sublimates and doesn't melt at normal pressures. For example, the US Department of Energy's Ask a Scientist program states "Since elemental iodine sublimes rather than melts, there is no such thing as 'liquid iodine.'".
Clackamas Community College, presents a distance learning exercise, purports to demonstrate the sublimation of iodine, even though the second picture of the series (at left) looks like it has a small bit of liquid iodine in it. This is one of the problems of canned chemistry labs - you don't get to observe the actual event, and so just take the word of whoever put the exercise together, even if it's wrong.
This real exercise from the Colorado School of Mines does the same thing as the Clackamas lab, but since it relies on actual measurements, leads to an understanding of why the liquid phase of iodine is often not seen. Science classes, especially chemistry classes need to be real labs. Sometimes for perceived safety issues or to save money, many schools are using canned or simulated labs. This is teaching science as dogma, rather than as a method of understanding observations.
