CHAPTER X 

 ADSORPTION 



As we turn from one physical force to another which is opera- 

 tive in hving systems, each appears to be more important than 

 the other, either in reaUty or because more attention has been 

 paid to it. Adsorption has certainly received its share, if not 

 a major share, of attention. This is in large measure due to 

 the application of colloidal principles to biological problems. 

 While possibly, as in the case of surface tension, there has been 

 too much confidence in theories, it is nevertheless true that 

 adsorption is a phenomenon of wide occurrence in the living as 

 well as in the nonliving world. Adsorption has to do with sur- 

 face, and it is at surfaces that chemical reactions take place; 

 the former is in many instances the precursor, if not the deter- 

 miner, of the latter. As protoplasm offers many surfaces (the 

 protoplasmic emulsion alone is responsible for innumerable 

 boundaries), then adsorption must play a large role in the activ- 

 ities of the living cell, simply because of the chemical reactions 

 that it initiates. 



White cotton material dipped in a dye assumes the color of the 

 dye if conditions are favorable. The union between the cotton 

 and the dye may be a weak one, as when one washing severs it; 

 or a firm one, if repeated washings do not sever it. In the first 

 case, a bond of some sort must have been established; otherwise 

 the cotton could not have taken the dye out of its solution. In 

 the second case, though the bond was a firm one, there is no con- 

 clusive evidence that a new chemical compound was formed. 

 The dye appears merely to be securely held at the surface of the 

 cotton without having gone into chemical combination with it. 

 This phenomenon is adsorption, or surface condensation. The 

 substance at the surface of which adsorption takes place is the 

 adsorbent. (Surface here means not only the visible outer surface 

 but the infinitely greater inner surface of all the minute pores or 

 particles which form the porous structure of the adsorbent.) 



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