Thus far we have examined titrimetric methods based on acid–base, complexation, and redox reactions. A reaction in which the analyte and titrant form an insoluble precipitate also can form the basis for a titration. We call this type of titration a pre- cipitation titration.
One of the earliest precipitation titrations, developed at the end of the eigh- teenth century, was for the analysis of K2CO3 and K2SO4 in potash. Calcium nitrate, Ca(NO3)2, was used as a titrant, forming a precipitate of CaCO3 and CaSO4. The end point was signaled by noting when the addition of titrant ceased to generate ad- ditional precipitate. The importance of precipitation titrimetry as an analytical method reached its zenith in the nineteenth century when several methods were de- veloped for determining Ag+ and halide ions.