240 HYDROGEN ION CONCENTRATION 



confusion. For this concept of acid, base, etc., is bound up with the 

 property of electric conductance in aqueous solutions. Tliis property, 

 to be sure, does not entirely disappear in our non-mole cularty dis- 

 persed substances, and we shall shortly recognize its share in con- 

 ductance phenomena under the form of electrophoresis. But in order 

 to avoid any possible confusion it would be better to restrict the use 

 of the terms "acid, base, ampholyte, salt" for the water-soluble, 

 true electrolytes, and the non-molecularty dispersed substances 

 which, because of their capacity to adsorb OH-ions, are analogous 

 to acids will be designated as acidoids. The following definitions 

 are given : 



An acidoid is a non-molecularly dispersed substance which adsorbs 

 OH-ions (or dissociates off H-ions) while maintaining a negative 

 charge (or adsorbs H-ions on neutralization of its negative charge). 

 A basoid is analogously defined, and charcoal is a good example of an 

 ampJiolytoid. Between a true acid (or base, or ampholyte) and a 

 coarsely dispersed acidoid (or basoid, or ampholytoid) the colloidal 

 substances form a multitude of intermediate stages. 



In adsorbing a dissolved base an acidoid forms a salt-like surface 

 compound which we shall designate as a saloid. Charcoal, being an 

 ampholytoid, forms saloids, with acids as well as with bases. In 

 addition, behaving like a true ampholyte, charcoal forms with KCl 

 a double saloid, just as an aixiino acid, at least in its sohd state, 

 forms a double salt compound with KCl. Also, quite analogously, 

 the tendency of charcoal to combine with HCl or NaOH is much 

 greater than that of combining with KCl, just as in the case of an 

 amino acid. 



The author is aware of the fact that the consideration of the so- 

 called "chemically unreactive" substances and of ampholytes under 

 a common heading will not meet with universal acceptance, and that 

 the phenomenon of adsorption will be regarded for a long time to 

 come in the light of a process quite distinct from those of ordinary 

 chemical reactions. In the age of the atomic model and of the re- 

 duction of chemical affinity and of the forces of cohesion to a common 

 basis of electrostatic forces, it would appear quite appropriate to do 

 away with such hmitations. Henceforth, then, in spealdng of ad- 

 sorption processes, it should be clearly understood that they do not 

 represent a fundamental contrast to chemical union. Since we can only 

 speak of adsorption when the reaction is hmited to the boundary sur- 



