stone and potter's clay must contain more earth.
The nature of oil presents the greatest problem. If water
preponderated in it, cold ought to solidify it; if earth
preponderated, then fire ought to do so. Actually neither
solidifies, but both thicken it. The reason is that it is full of
air (hence it floats on the top of water, since air tends to rise).
Cold thickens it by turning the air in it into water, for any
mixture of oil and water is thicker than either. Fire and the lapse of
time thicken and whiten it. The whitening follows on the evaporation
of any water that may have been in it; the is due to the change of the
air into water as the heat in the oil is dissipated. The effect in
both cases is the same and the cause is the same, but the manner of
its operation is different. Both heat and cold thicken it, but neither
dries it (neither the sun nor cold dries oil), not only because it
is glutinous but because it contains air. Its glutinous nature
prevents it from giving off vapour and so fire does not dry it or boil
Those bodies which are made up of earth and water may be
classified according to the preponderance of either. There is a kind
of wine, for instance, which both solidifies and thickens by boiling-I
mean, must. All bodies of this kind lose their water as they That it
is their water may be seen from the fact that the vapour from them
condenses into water when collected. So wherever some sediment is left
this is of the nature of earth. Some of these bodies, as we have said,
are also thickened and dried by cold. For cold not only solidifies but
also dries water, and thickens things by turning air into water.
(Solidifying, as we have said, is a form of drying.) Now those
things that are not thickened by cold, but solidified, belong rather
to water, e.g.. wine, urine, vinegar, lye, whey. But those things that
are thickened (not by evaporation due to fire) are made up either of
earth or of water and air: honey of earth, while oil contains air.
Milk and blood, too, are made up of both water and earth, though earth