In the experiment of the block of ice that in the beginning is 10
degrees below the freezing point, as shown by the thermometer, the
molecules have a definite intensity of motion. The intensity of this
motion increases when heat is applied until it reaches 32 degrees, when
it remains stationary until all of the ice is melted. At this point
there is a rearrangement of the molecules of water as it assumes the
liquid state. To perform this rearrangement requires a certain amount of
work done, which is analogous to the winding up of a weight to a certain
distance. There has been energy used in winding up the weight, but that
energy now is not destroyed, nor still in the form of heat, but is in
the potential state--ready to do some other kind of work. So, the heat
that has been applied to the melting ice has been utilized during the
process of its liquefaction in rearranging the water molecules and
putting them in a state of strain, so to speak, like the weight that is
wound up to a certain height. There is a certain amount of potential
energy that is stored in the molecules of water that will be given up
and become active energy in the form of heat, if the water is again
frozen. To melt a cubic foot of ice requires as much heat as it would
to raise a cubic foot of water 144 degrees Fahrenheit. But, as we have
seen, while all of this energy is absorbed as heat, it is not lost as
energy. It ceases to be kinetic or active and becomes potential energy.
This (let us repeat) has been called latent heat. The term grew out of
the old idea that heat was a fluid and that when it became latent it hid
itself away somewhere in the interatomic spaces of matter and ceased to
be longer sensible heat. It came into existence in the same manner and
occupies the same place in the science of heat that the word "current"
does in the science of electricity: both of them are misnomers.

When the ice is all melted potential energy is no longer stored, but is
manifested in the sensible heating of water, the degree of which is
measurable by the thermometer, until it reaches the boiling point, where
it is again arrested. All of the surplus heat above that temperature is
consumed in rending the liquid water into moisture globules that float
away into the air, each one of them charged with a store of potential
energy. Let us follow this vapor spherule as it floats into the upper
regions of the atmosphere. Myriads of its fellows travel with it until
it