As they listened to Professor Holmes’ long lecture, the students were beginning
to get restless. It had started to drizzle when the professor started his
lecture but now there was a heavy downpour. Some of the students had been
so distracted that their minds had begun to wander. Even Professor Holmes
was distracted because what had begun as rain pitter-pattering on the roof was
now making it difficult for his class to hear him.
“On a rainy day like today, I think I know exactly what you are all thinking
about. You would rather be curled up in bed, maybe reading a favorite book
or simply gathered in the living room chatting with your families. Doesn’t rain
make you melancholic sometimes?”
But before any of his students could answer, Professor Holmes snapped
back into lecture mode.
“So much for idle talk. Let me continue. I was talking about reaching the
liquid water…”
“Oh, I see that we were moving into the liquid region. What a fascinating
liquid indeed! I know you are all eager to go home but we have to finish our
discussion as this will be included in your exams.”
“In the liquid region, we again recover two degrees of freedom. You should
remember by now that ‘two degrees of freedom’ is a scientist’s way of saying,
within this context, that we can change both pressure and the temperature
independently, i.e., move right or left, up or down, and still observe only one
phase.”
“Suppose that from point Y we increase the pressure and reached point C in
the region denoted ‘liquid’ in the phase diagram. We can go in two directions,
which will allow us to encounter two different phenomena. We can go straight
upwards and encounter some new forms of ice, but we do not need to explore
those regions of extremely high-pressure forms of ice. When I say ice, I do not
mean the same ice that you regularly encounter every day. I am referring to a
different kind of ice; in fact, there are more than seven different crystals of ice.
These ices ‘live’ only at extremely high pressures and are certainly not relevant
to life!”
“Instead, we shall move to the right in the phase diagram and increase the
temperature keeping the pressure fixed. We do that by heating the system;