218 CHEMISTRY OF PLANT LIFE 



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 carbo- 

 hydrates, 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 cata- 

 lysts. 



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 mate- 

 rials 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 indus- 

 trial 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; the prevention of the smoke nuisance by electric 



