he energy
to overcome the chemical resistance to the molecular rearrangement which
constitutes the reaction itself. Evidence in favor of the accuracy of this
view of the nature of the catalytic action of colloidal substances is
afforded by the facts that catalysts accelerate the velocity of reversible
reactions in either direction and that they do not change the point of
final equilibrium, in any case; that is, they do not affect the nature or
direction of the reaction, but only accelerate a chemical change which
would otherwise take place more slowly because of the stability (or
chemical resistance) of the molecules involved, or their inability to come
quickly into intimate molecular contact.

These facts and principles have been clearly established in many studies of
the nature of enzyme action (enzymes are typical colloidal catalysts) and
probably apply equally well to the action of other types of colloidal
catalysts. On the other hand, the catalytic action of certain inorganic and
non-colloidal substances, such as the action of acids in accelerating the
hydrolysis of carbohydrates, etc., may be conceived to be due to chemical
influences upon the internal molecular resistance, which are similar in
their effects, but entirely different in their mechanism, from the physical
effects of the surface boundary phenomena of the colloidal catalysts.

INDUSTRIAL APPLICATIONS OF COLLOIDAL PHENOMENA

Large numbers of industrial processes are based upon colloidal phenomena.
Many of these processes were known and practiced long before the nature of
the phenomenon itself was understood. But with the coming of the knowledge
of the nature, causes, and possibilities of the control, of the colloidal
condition of the materials involved, immense improvements in the economy of
the process, or the quality of the end-products, have been worked out, in
many cases. Many volumes of treatises concerning the industrial
applications of colloidal phenomena have been written. Any discussion of
these would be out of place here; but the following list of examples will
serve to illustrate the immense importance of these matters both in
industry and to the needs of everyday life: the tanning of leather; the
dyeing of fabrics; vulcanizing rubber; mercerizing cotton; sizing textile
fabrics; manufacture of mucilages and glues; manufacture of hardened casein
goods; manufacture of celluloid; production of colloidal graphite for
lubrication;