SECTION II.: CELLULAR MECHANICS 



CHAPTER VII 



IONISATION 



IONS THE WORKMEN OF THE CELL 



" Many things move me to suspect that everything [natural as well as 

 mechanical] depends upon certain forces, in virtue of Which the particles of 

 bodies, through forces not yet understood, are either impelled together . . . , 

 or are repelled and recede from one another." NEWTON. 



THIS subject has been alluded to in connection with abnormal 

 osmotic pressures (Chap. V. p. 44), where it was pointed out 

 that electrolytes, on going into solution, were more or less dis- 

 sociated into their constituent ions. The extent to which an 

 electrolyte is thus dissociated determines whether it is a strong 

 or a weak electrolyte. Inorganic acids and bases and their 

 salts are almost completely dissociated in solution, the dissociation 

 increasing with dilution until, of course, complete dissociation is 

 reached. Organic acids and bases, as a rule, are dissociated 

 with difficulty, complete dissociation being reached only at great 

 dilutions. There are exceptions, some organic bases are just as 

 well ionised as the strongest inorganic bases. Guanidin salts, 

 for instance, have dissociation values lying between sodium and 

 barium salts. Salts formed of a weakly dissociated acid and 

 a strongly dissociated base or of a weak base and a strong 

 acid have dissociation values intermediate to those of their 

 constituents. 



There are two outstanding points of interest about ions. 



1. Ions are always electrically charged. The " metal " ion 

 having a positive and the " acid " ion a negative charge. (The 

 former, in Faraday's terminology, is called a cation and the latter 

 an anion.) 



2. Ions are never free, but are always hydrated. 



B.B. 49 4 



