ADSORPTION 179 



molecules, or, shall we say, molecules are polar because of this 

 electric difference. Such forces are attractive and may be 

 responsible for adsorption phenomena. Briefly and broadly 

 put, surfaces are electrically charged and therefore attract and 

 hold substances of opposite charge (Figs. 80, 177). 



That electric charge, in the form of stray fields of electromag- 

 netic forces surrounding molecules, plays an important role in 

 adsorption is evident in the behavior of substantive and adjective 

 dyes. Acid fuchsin is negatively and basic fuchsin positively 

 charged; the one or the other, not both, is usually adsorbed by 

 an adsorbent; for example, kaolin is negative, and aluminum 

 positive; the former adsorbs only positively charged (basic) dyes, 

 and the latter only negatively charged (acid) dyes. In dyeing 

 cotton cloth, where the fibers and the desired dye are of the same 

 charge, a "mordant" of opposite charge is first added. It is 

 adsorbed by the fibers and confers on them a charge of opposite 

 sign, i.e., the sign of the mordant. An acid solution gives the 

 fibers a positive charge, and an alkaline solution gives them a 

 negative charge. The dye of opposite charge is then readily 

 taken on. 



While forces expressed by coordination numbers present the 

 most satisfactory interpretation of adsorption, undoubtedly 

 other forms of attraction are involved, such as have been char- 

 acterized as residual valence and forces of the nature of those of 

 van der Waals. 



Adsorption in Life. — Few phenomena characterize vital 

 processes more than does adsorption. Freundlich states 

 that poisoning may be due to adsorption which follows his 

 adsorption isotherm. He had in mind the taking up of veratrine 

 by the marine snail Aplysia. We are more interested in ourselves 

 than we are in marine snails, so let us carry this identical problem 

 over to human physiology and consider O. Warburg's adsorption 

 theory of narcosis and anesthesia. The theory had been previ- 

 ously advanced by Traube and Czapek. 



Following up some experiments of Freundlich's on the adsorp- 

 tion of oxalic acid by blood charcoal, Warburg, in searching for a 

 possible explanation, found that oxidation of the oxalic acid into 

 carbon dioxide and water takes place. He then proved that this 

 inanimate oxidation process can be retarded by narcotics just 

 as animate oxidation, i.e., respiration, is retarded by them. 



