SOLUTION TO EXERCISE 10

(a) For water's phase diagram, the slope of the solid-liquid border
is negative - that is, as the pressure increases, the temperature decreases.
For carbon dioxide, the slope is positive - as pressure increases, temperature
increases.

(b) The first block, the one on the bottom, feels pressure from the weight of
the second block on top of it.  According to the phase diagram for water, 
the melting point of water decreases as the pressure increases.  Since the
temperature has not changed, the first block is more likely to melt because
it is now closer to its melting point.  In fact, the bottom of the first block
is more likely to melt than the top.

(c) The first block of dry ice (solid carbon dioxide) feels pressure from the
weight of the second block on top of it.  Unlike water, however, the melting
point of carbon dioxide increases as the pressure increases.  So the second
block is more likely to melt.  The top of the second block is more likely
to melt than the bottom.