Six types of cells using zinc sulphate alone and zinc sulphate mixed with potassium sulphate, with and without liquid junction potentials, have been studied in order(i) to test whether activity coefficient of single ions can be roughly calculated and used in the study of equilibria, (ii) to see if Zn(SO4)22- ions are present in zinc sulphate solutions upto 0.1 M and (iii) to measure the value of dissociation constant(K) of zinc sulphate into zinc and sulphate ions. The conclusion regarding (i) is positive and (ii) is negative. Values of K are given by all the cells. The most probable value obtained from Hgy Znx I ZnSO4 Hg2SO4 I Hg, by extrapolating the value to zero concentration is 7.5 X 10-3.