ON SOME FEATURES OF THE TITRATION CURVES OF CARBONIC ACID AND PHOSPHORIC ACID WITH BARYTA

Some hitherto unpublished features of potentiometric and conductometric titration curves of carbonic acid and (ortho) phosphoric acid with baryta have been presented and their significance, in the ligbt of the Mass Action principle anal the Phase Rule, pointed out. During the titration of carbonic acid, precipitation of BaCO3 starts from a point where the conductometric titration curve show; a sharp maximum. Precipitation of the carbonate causes an overlapping of the two stages of disscciation and neutralisation of carbonic acid, and only the total quantity of H2CO3 is indicated by the titrati pn curve. In the case of phosphoric acid, however, three stages of neutralisation, each culminating in a marked inflexion or break in the titration curve, are clearly indicated for additions of baryta corresponding to the first, the second and the third equivalent of the acid. The monohydrogen phosphate starts getting precipitated when exactly one equivalent of the base has been added. Between the second and the third equivalent of the added base, the fr$ and the conductivity remain practically constant. It has been shown that this follows from the Phase Rule remembering that, during the addition of the third equivalent, two solid phases, viz., those of the monohydrogen phosphate and the normal phosphate, coexist