come into contact; and the second is that required for the
molecular rearrangement which constitutes the reaction. Clearly, the time
required for the substances to come into molecular contact will be greatly
diminished if they are mutually adsorbed in large quantities on the
extended surface area of some colloidal catalyst which is present in the
mixture rather than scattered throughout its entire volume. The application
of this principle to the catalysis of hydrolytic reactions is not apparent,
if it is considered that the H_{2}O molecules which cause the hydrolysis
are those of the solvent itself; but is clear on the assumption (which is
discussed in the following chapter) that the water which enters into a
colloidal complex is in multimolecular form, represented by the formula
(H_{2}O)_{_n_}, in which the oxygen atoms are quadrivalent and, hence, much
more active chemically than as illustrated in the simple solvent action of
water.

Hence, the surface adsorption of reacting bodies by a colloidal catalyst
may have a very important influence in decreasing the time required to
bring the reacting molecules into intimate contact, and so increasing the
velocity of the reaction.

But the colloidal condition of the catalyst may also aid in decreasing the
"chemical resistance" which tends to slow up the reaction. Chemical
resistance may be understood to be the internal molecular friction of the
densely packed atoms within the reacting molecule, which tends to prevent
the molecular rearrangement and so to prolong the second period of the
reaction time. To overcome this friction and so decrease the reaction time,
some form of energy is necessary. If there be present in the solution in
which the reaction is taking place some colloidal catalyst, and if the
reacting bodies are concentrated at the surface boundaries between the two
phases of the colloidal system, they may be conceived to be within the
sphere of influence of the surface energy of the dispersed particles of the
catalyst, so that this may furnish the energy necessary to overcome the
chemical resistance of the reacting bodies, and so to speed up the second
portion of the reaction time.

From these considerations, it would appear that the colloidal condition of
such catalysts as enzymes, etc., has much to do with their ability to
increase reaction velocities, both by reducing the time necessary for the
reacting bodies to come into molecular contact and by furnishing t