66 MOLECULAR WEIGHT AND POLYMERISM 



Electrolytes luhicTi follow Ostivald's law of dilution. For 

 a dissociation in a dissolved electrolyte in the sense of the 

 equation 



KN0 3 = (K) + (N0 3 ), 

 i. e. an equilibrium symbolized by 



if the ions are treated as molecules it seems an inevitable 

 consequence of the equation of equilibrium already ar- 

 rived at, 



2 n log C const., 

 that 



the concentration of the two systems being taken with 

 opposite signs ; this may be written 



or if V be the volume in litres of one gram-molecule (reci- 

 procal of the normality), 



~ I a ^ p + a n 



whence 



(i a) V MooO^oo P)'* 



However, for salts, e. g. nitre, this relation does not hold, 

 as we shall see later, but only for a definite though very 

 numerous group of electrolytes, viz. acids and bases in 

 aqueous solution, that decompose in the manner 



ZH = (Z) + (iff) and MOH = (M) + (OH) 9 



and of these only the weak acids and bases. The law 

 seems to be restricted to cases in which the dissociation 

 yields ions of the solvent water, and then only when their 

 concentration is small. 



