r extra
valences of other substances with which the water is brought into contact,
and so cause the latter to enter into solution. All kinds of substances
dissolve in water, and when in solution, or even when only moistened, are
much more active chemically than when dry. This property of water
contributes greatly to the possibilities of the chemical reactions which
constitute life processes.

Water, likewise, has a higher dielectric constant than any other common
liquid. This means that it does not readily conduct electricity, or readily
permit electric equilibrium to be established in it; or, in other words,
that it is a good insulator. This property permits the existence in it
simultaneously of materials having opposite electric charges, or the
so-called ionization phenomena; hence, water is the best-known ionizing
medium, and ionization favors chemical reactivity.

Again, water has a very high specific heat, a fact which is of the utmost
biological importance. It takes more heat to raise the temperature of one
gram of water through one degree than is required to produce the same
result in any other known substance; or, stated the other way around, a
given amount of heat will cause less change in temperature of water than of
any other known substance. Further, the latent heat of liquefaction and of
vaporization (i.e., the amount of heat required to change the substance
from solid to liquid and from liquid to gaseous state, respectively) is
greater for water than for any other common substance. These facts are of
very great importance in cell-protoplasm. The high specific heat of water
provides that the heat liberated by the chemical reactions which take place
in the protoplasm can be absorbed by the water of the cell contents, and
given off again to other reactions, with very slight effect upon the
temperature of the protoplasm itself. Hence, violent changes in
temperature, which might be disastrous to the life of the cell, are
prevented by the high specific heat of the water which it contains.
Similarly, the high latent heat of liquefaction of water, resulting in the
giving up of large quantities of heat before it can become solid, or
"freeze," tends to prevent freezing and thawing of the cell contents with
sudden changes of external temperatures at or near the freezing temperature
of water.

As a result of its physical properties, as just briefly described, water
accelerates all kinds of chemical reactions in prot