In view of the fact that the acids used in the inquiries discussed in Part XII and the succeeding parts of these studies were all monobasic, it was desirable to investigate the hydrolytic activity of a dibasic acid, more especially with a view to following the progressive alteration in molecular hydrolytic activity and apparent degree of hydration attending changes of concentration. A series of experiments, using sulphuric acid as the catalyst, has been carried out therefore on the lines of those described in Part XII. Some of the complexities of the hydrolytic process and of the polarimetric method of following its course were dealt with in that communication; moreover, several disturbing factors were referred to, such as the change in the osmotic conditions as the action proceeds and changes in the optical activity of the various substances due to dilution, to their mutual interference, and to the influence of acids or salts; the possible influence of “mutarotation,” however, was not mentioned, as there appeared to be no reason to believe that it in any way affected the results. The study of the rates at which hydrolysis is effected by sulphuric acid of different degrees of concentration has shown that exactly the same complexities are met with in this case as were experienced in the case of chlorhydric and nitric acids. Thus, in the more concentrated solutions, there is a gradual change in the final angle of rotation after hydrolysis is complete such as was observed in the inquiry described in Part XII; this was allowed for as before when necessary, though in most of the experiments the concentration was not great enough for its effect to be noticed.