Isohydric solution
If the concentration of the common ions in the solution of two electrolytes , for example 
ion concentration in 
and 
or 
ion concentration in 
and 
is same, then on mixing them there is no change in the degree of dissociation of either of the electrolytes. Such solutions are called isohydric solutions.
Consider two isohydric solutions of acids 
and
. Let 
and 
be their dilutions and 
and 
be their degree of dissociation at the respective dilution. Then,
Above equation is useful for calculating the relative dilution of two acids at which they would be isohydric.