30-i Gooch and Danner — Points in the Interaction of 



sulphuric acid, that the amount of decomposition is greater as 

 the time of action is extended, and that increase of tempera- 

 ture heightens the change. We note in particular, for exam- 

 ple, that the presence of ten per cent of [1 : 1] sulphuric acid 

 induces at the ordinary temperature no immediate decomposi- 

 tion of the permanganate, none in eight hours, and a breaking 

 down amounting to four per cent in five days ; and that the 

 presence of fifty per cent of acid of the same strength occa- 

 sions the decomposition of about two per cent at once, fifteen 

 per cent in eight hours, and more than half the entire amount 

 of permanganate in the course of five days. It is evident 

 also that twenty per cent of the [1 : 1] acid produces no 

 appreciable effect at ordinary temperatures and under expo- 

 sures of a few hours only. The effect of heating the mixture 

 of acid and permanganate to 80° C. for an hour and a half 

 is closely- comparable with that brought about by the live days 

 action at the ordinary temperature. 



In another series of similar experiments, the detailed record 

 of which we omit as unnecessary, the absolute amounts of 

 liquid and acid were increased while the proportion of the 

 latter to the whole volume of the former was preserved. The 

 volume of the liquid containing the acid and permanganate 

 was fixed at 100 cm 3 and the absolute amounts of acid were 

 taken five times as great as those used at corresponding points 

 of the preceding series. The amounts of decomposition ob- 

 served in these experiments followed those of the first series 

 so closely as to compel the conclusion that it is the proportion 

 of acid present rather than the absolute amount which is 

 chiefly influential in the decomposition of the permanganate 

 under given conditions. In still another series of experiments 

 which differed from the last in the single point that the 

 amount of permanganate used was increased five-fold no appre- 

 ciable differences in effect which might be traced to such 

 extra use of permanganate were discoverable. 



It is, of course, possible, and even probable, that some 

 decomposition of the permanganate by the sulphuric acid 

 might be brought about after the addition of the oxalic acid 

 during the warming of the mixture up to the temperature at 

 which the oxalic acid and permanganate interact. The experi- 

 ments of Table II were therefore undertaken to test this 

 point. In them oxalic acid was replaced by a solution of fer- 

 rous sulphate in order to secure the removal of the residual 

 permanganate at ordinary temperatures. The greatest care 

 was taken to guard against atmospheric oxidation during the 

 course of the experiment. The solution of ferrous sulphate 

 was standardized before and after making the test experiments 

 and found to be unchanged during the period of work. In 



